From 16dba11b21dc77bc4a79b9eca9037c5a4a6f3d7a Mon Sep 17 00:00:00 2001
From: Fabian Montero <fabian@posixlycorrect.com>
Date: Wed, 25 Mar 2026 20:48:30 -0600
Subject: [PATCH] triforce-strategies: add S&P 500 vs anythingn calculator

claude helped with this
---
 CLAUDE.md                                     |  31 +-
 content/triforce-strategies/tools/_index.md   |   5 +
 .../tools/snp500_vs_anything.md               |  41 ++
 static/css/fund-comparison.css                | 181 ++++++
 static/js/fundComparison.js                   | 567 ++++++++++++++++++
 templates/shortcodes/fund_comparison.html     | 146 +++++
 6 files changed, 969 insertions(+), 2 deletions(-)
 create mode 100644 content/triforce-strategies/tools/_index.md
 create mode 100644 content/triforce-strategies/tools/snp500_vs_anything.md
 create mode 100644 static/css/fund-comparison.css
 create mode 100644 static/js/fundComparison.js
 create mode 100644 templates/shortcodes/fund_comparison.html

diff --git a/CLAUDE.md b/CLAUDE.md
index 0c3c3b2..c9d8098 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -10,9 +10,12 @@ Personal homepage built with Zola.
 - `content/` — Markdown content
   - `blog/` — Blog posts
   - `lib/` — Library/reference articles
-  - `triforce_strategies/` — Triforce Strategies LLC content
+  - `triforce-strategies/` — Triforce Strategies LLC content
+    - `tools/` — Interactive calculators/tools
+- `templates/shortcodes/` — Custom shortcodes (override theme)
+- `static/js/` — JavaScript files
+- `static/css/` — CSS files
 - `themes/tabi-lean/` — Theme (git subtree, do not edit directly)
-- `static/` — Static assets
 - `config.toml` — Site configuration
 
 ## Content Conventions
@@ -20,5 +23,29 @@ Personal homepage built with Zola.
 - Section indices: `_index.md`
 - Internal links: `@/path/to/file.md`
 
+## Adding Interactive Tools
+
+To add a new tool under `triforce-strategies/tools/`:
+
+1. **Create shortcode**: `templates/shortcodes/tool_name.html`
+   - HTML structure (form, canvas, results container)
+   - Load JS via `{{ get_url(path='js/toolName.js') | safe }}`
+   - Include `<noscript>` fallback
+
+2. **Create JS**: `static/js/toolName.js`
+   - Wrap in IIFE: `(function() { 'use strict'; ... })();`
+   - Use theme CSS variables for colors (--text-color, --primary-color, etc.)
+   - Scale canvas for retina: `window.devicePixelRatio`
+
+3. **Create CSS**: `static/css/tool-name.css`
+   - Use theme CSS variables from `themes/tabi-lean/sass/main.scss`
+   - Responsive layout with media queries
+
+4. **Create page**: `content/triforce-strategies/tools/tool_name.md`
+   - Frontmatter: `[extra] stylesheets = ["css/tool-name.css"]`
+   - Invoke shortcode: `{{ tool_name() }}`
+
+Example: `snp500_vs_anything` (fund comparison calculator with Monte Carlo simulation)
+
 ## Commit Style
 `type: description` (e.g., `blog: add post title`)
diff --git a/content/triforce-strategies/tools/_index.md b/content/triforce-strategies/tools/_index.md
new file mode 100644
index 0000000..663f48d
--- /dev/null
+++ b/content/triforce-strategies/tools/_index.md
@@ -0,0 +1,5 @@
++++
+title = "tools"
+sort_by = "title"
+paginate_by = 10
++++
diff --git a/content/triforce-strategies/tools/snp500_vs_anything.md b/content/triforce-strategies/tools/snp500_vs_anything.md
new file mode 100644
index 0000000..4cd742a
--- /dev/null
+++ b/content/triforce-strategies/tools/snp500_vs_anything.md
@@ -0,0 +1,41 @@
++++
+title = "S&P 500 vs lo que sea"
+date = 2026-03-25
+description = "Compara el crecimiento del S&P500 contra cualquier otro fondo hipotético usando una simulación Monte Carlo sencilla."
+
+[extra]
+stylesheets = ["css/fund-comparison.css"]
++++
+
+Esta calculadora compara el crecimiento proyectado del S&P500 contra cualquier otro fondo hipotético. Usa una simulación Monte Carlo sencilla para modelar la volatilidad del mercado.
+
+Este tipo de simulación es muy sencilla y solo sirve para ilustrar la diferencia entre el rendimiento del S&P500 en comparación a otros fondos disponibles en Costa Rica.
+
+## Cómo usar la calculadora
+
+0. **Idioma**: Perdón, todo está en spanglish, pero es que es el restulado de una investigación que es en inglés y español.
+1. **Fondo S&P 500**: Valores por defecto representan un índice de bajo costo. Puede buscar el rendimiento real del S&P 500 y poner los valores aquí.
+2. **Fondo a comparar**: Introduzca los parámetros del fondo que quiere comprarar.
+3. **Parámetros de inversión**: Seleccione el tiempo de la inversión y la contribución mensual.
+4. **Monte Carlo**: Active la simulación para un modelado rudimentario de volatilidad.
+
+## Cómo leer el gráfico generado
+
+- **Medianas**: Verde (S&P 500) y azul (fondo comparado) muestran los resultados esperados
+- **Bandas sombreadas**: Rango del percentil 10 al 90 cuando la simulación Monte Carlo está activada
+- **Δ (Delta)**: Diferencia entre los valores finales de ambos fondos
+- **Tax loss**: (pérdida fiscal) Segmento rojo que muestra el impuesto sobre ganancias de capital deducido al retirar (cuando aplica)
+
+### Nota acerca de impuestos
+- Costarricenses no tienen que pagar impuestos a ganancias de capital obtenidas a través de inversinoes directas en USA. Más info: [taxation of NRAs](https://www.irs.gov/businesses/taxation-of-nonresident-aliens-international-tax-gap-series). 
+- En Costa Rica no hay renta global (aún lol)
+- Por eso la calculadora no calcula una pérdida fiscal al invertir directamente en el S&P500 pero sí al invertir en un fondo de CR.
+
+{{ fund_comparison() }}
+
+## Notas generales
+- Los rendimientos se modelan usando distribución log-normal
+- Los gastos de administración y comisiones se deducen mensualmente
+- El impuesto sobre ganancias de capital se aplica únicamente sobre las ganancias al momento del retiro final y se muestra como una caída roja en el gráfico
+- Los rendimientos históricos del S&P 500 promedian ~10% anual con ~15% de desviación estándar
+- Rendimientos pasados no garantizan resultados futuros
diff --git a/static/css/fund-comparison.css b/static/css/fund-comparison.css
new file mode 100644
index 0000000..a9980eb
--- /dev/null
+++ b/static/css/fund-comparison.css
@@ -0,0 +1,181 @@
+.fund-comparison-container {
+    width: 100%;
+}
+
+.fund-comparison-form {
+    display: grid;
+    grid-template-columns: 1fr 1fr;
+    gap: 1.5rem;
+    margin-bottom: 2rem;
+}
+
+.form-section {
+    background: var(--bg-0);
+    padding: 1rem;
+    border-radius: 4px;
+}
+
+.form-section h3 {
+    margin-top: 0;
+    margin-bottom: 1rem;
+    color: var(--text-color-high-contrast);
+    font-size: 1rem;
+}
+
+.form-group {
+    margin-bottom: 0.75rem;
+}
+
+.form-group label {
+    display: block;
+    margin-bottom: 0.25rem;
+    font-size: 0.85rem;
+    color: var(--meta-color);
+}
+
+.form-group input {
+    width: 100%;
+    padding: 0.5rem;
+    background: var(--bg-2);
+    border: 1px solid var(--divider-color);
+    border-radius: 3px;
+    color: var(--text-color);
+    font-family: var(--code-font);
+    font-size: 0.9rem;
+    box-sizing: border-box;
+}
+
+.form-group input:focus {
+    outline: none;
+    border-color: var(--primary-color);
+}
+
+.form-section-full {
+    grid-column: 1 / -1;
+}
+
+.form-row {
+    display: grid;
+    grid-template-columns: 1fr 1fr;
+    gap: 1rem;
+}
+
+.checkbox-group {
+    display: flex;
+    align-items: center;
+    gap: 0.5rem;
+    margin-top: 0.5rem;
+}
+
+.checkbox-group input[type="checkbox"] {
+    width: auto;
+}
+
+.checkbox-group label {
+    margin-bottom: 0;
+}
+
+.calculate-btn {
+    display: block;
+    width: 100%;
+    padding: 0.75rem;
+    margin-top: 1rem;
+    background: var(--primary-color);
+    color: var(--background-color);
+    border: none;
+    border-radius: 4px;
+    font-family: var(--sans-serif-font);
+    font-size: 1rem;
+    font-weight: 550;
+    cursor: pointer;
+    transition: opacity 0.2s;
+}
+
+.calculate-btn:hover {
+    opacity: 0.9;
+}
+
+.chart-container {
+    margin-bottom: 2rem;
+    background: var(--bg-2);
+    border-radius: 4px;
+    padding: 1rem;
+}
+
+.chart-container canvas {
+    width: 100%;
+    display: block;
+}
+
+.summary-section {
+    margin-bottom: 1.5rem;
+}
+
+.summary-section h3 {
+    margin-top: 0;
+    margin-bottom: 1rem;
+}
+
+.summary-table {
+    width: 100%;
+    border-collapse: collapse;
+    font-size: 0.9rem;
+}
+
+.summary-table th,
+.summary-table td {
+    padding: 0.5rem 0.75rem;
+    text-align: left;
+    border-bottom: 1px solid var(--divider-color);
+}
+
+.summary-table th {
+    background: var(--bg-0);
+    font-weight: 550;
+}
+
+.summary-table td:not(:first-child) {
+    text-align: right;
+    font-family: var(--code-font);
+}
+
+.percentiles-details {
+    margin-top: 1rem;
+}
+
+.percentiles-details summary {
+    cursor: pointer;
+    color: var(--primary-color);
+    font-weight: 550;
+}
+
+.percentiles-table {
+    margin-top: 0.75rem;
+}
+
+.noscript-warning {
+    background: #ff9800;
+    color: #000;
+    padding: 1rem;
+    border-radius: 4px;
+    text-align: center;
+}
+
+@media (max-width: 600px) {
+    .fund-comparison-form {
+        grid-template-columns: 1fr;
+    }
+
+    .form-row {
+        grid-template-columns: 1fr;
+    }
+
+    .summary-table {
+        font-size: 0.8rem;
+    }
+
+    .summary-table th,
+    .summary-table td {
+        padding: 0.4rem 0.5rem;
+    }
+}
diff --git a/static/js/fundComparison.js b/static/js/fundComparison.js
new file mode 100644
index 0000000..ce802cb
--- /dev/null
+++ b/static/js/fundComparison.js
@@ -0,0 +1,567 @@
+(function() {
+    'use strict';
+
+    // Box-Muller transform for normal distribution
+    function boxMuller() {
+        let u1, u2;
+        do {
+            u1 = Math.random();
+            u2 = Math.random();
+        } while (u1 === 0);
+        return Math.sqrt(-2.0 * Math.log(u1)) * Math.cos(2.0 * Math.PI * u2);
+    }
+
+    // Convert annual rate to monthly
+    function annualToMonthly(annualRate) {
+        return Math.pow(1 + annualRate, 1/12) - 1;
+    }
+
+    // Run a single simulation
+    function runSimulation(params, months) {
+        const monthlyReturn = annualToMonthly(params.annualReturn);
+        const monthlyVol = params.annualVol / Math.sqrt(12);
+        const monthlyExpense = params.expenseRatio / 12;
+
+        let value = 0;
+        const values = [0];
+
+        for (let m = 1; m <= months; m++) {
+            // Add monthly deposit at start of month
+            value += params.monthlyDeposit;
+
+            // Apply log-normal return
+            const randomReturn = monthlyReturn + monthlyVol * boxMuller();
+            value *= Math.exp(randomReturn);
+
+            // Deduct expense ratio
+            value *= (1 - monthlyExpense);
+
+            values.push(value);
+        }
+
+        // Track pre-tax value
+        const preTaxValue = value;
+
+        // Apply capital gains tax at withdrawal if specified
+        const totalDeposits = params.monthlyDeposit * months;
+        const gains = value - totalDeposits;
+        let taxPaid = 0;
+        if (params.capitalGainsTax > 0 && gains > 0) {
+            taxPaid = gains * params.capitalGainsTax;
+            value -= taxPaid;
+        }
+
+        return { values, finalValue: value, preTaxValue, taxPaid };
+    }
+
+    // Run Monte Carlo simulation
+    function runMonteCarlo(params, months, numSimulations) {
+        const allFinalValues = [];
+        const allPreTaxValues = [];
+        const allTaxPaid = [];
+        const allValuesByMonth = [];
+
+        for (let i = 0; i <= months; i++) {
+            allValuesByMonth.push([]);
+        }
+
+        for (let sim = 0; sim < numSimulations; sim++) {
+            const result = runSimulation(params, months);
+            allFinalValues.push(result.finalValue);
+            allPreTaxValues.push(result.preTaxValue);
+            allTaxPaid.push(result.taxPaid);
+            for (let m = 0; m <= months; m++) {
+                allValuesByMonth[m].push(result.values[m]);
+            }
+        }
+
+        // Sort values at each month for percentile calculation
+        for (let m = 0; m <= months; m++) {
+            allValuesByMonth[m].sort((a, b) => a - b);
+        }
+        allFinalValues.sort((a, b) => a - b);
+        allPreTaxValues.sort((a, b) => a - b);
+        allTaxPaid.sort((a, b) => a - b);
+
+        // Calculate percentiles
+        function getPercentile(sortedArr, p) {
+            const idx = Math.floor(sortedArr.length * p);
+            return sortedArr[Math.min(idx, sortedArr.length - 1)];
+        }
+
+        const percentiles = {
+            p10: getPercentile(allFinalValues, 0.10),
+            p25: getPercentile(allFinalValues, 0.25),
+            p50: getPercentile(allFinalValues, 0.50),
+            p75: getPercentile(allFinalValues, 0.75),
+            p90: getPercentile(allFinalValues, 0.90)
+        };
+
+        const preTaxPercentiles = {
+            p50: getPercentile(allPreTaxValues, 0.50)
+        };
+
+        const taxPaidPercentiles = {
+            p50: getPercentile(allTaxPaid, 0.50)
+        };
+
+        // Get percentile curves for chart
+        const curves = {
+            p10: [],
+            p50: [],
+            p90: []
+        };
+
+        for (let m = 0; m <= months; m++) {
+            curves.p10.push(getPercentile(allValuesByMonth[m], 0.10));
+            curves.p50.push(getPercentile(allValuesByMonth[m], 0.50));
+            curves.p90.push(getPercentile(allValuesByMonth[m], 0.90));
+        }
+
+        return { percentiles, preTaxPercentiles, taxPaidPercentiles, curves };
+    }
+
+    // Run deterministic simulation (no volatility)
+    function runDeterministic(params, months) {
+        const monthlyReturn = annualToMonthly(params.annualReturn);
+        const monthlyExpense = params.expenseRatio / 12;
+
+        let value = 0;
+        const values = [0];
+
+        for (let m = 1; m <= months; m++) {
+            value += params.monthlyDeposit;
+            value *= (1 + monthlyReturn);
+            value *= (1 - monthlyExpense);
+            values.push(value);
+        }
+
+        const preTaxValue = value;
+        const totalDeposits = params.monthlyDeposit * months;
+        const gains = value - totalDeposits;
+        let taxPaid = 0;
+        if (params.capitalGainsTax > 0 && gains > 0) {
+            taxPaid = gains * params.capitalGainsTax;
+            value -= taxPaid;
+        }
+
+        return {
+            percentiles: { p10: value, p25: value, p50: value, p75: value, p90: value },
+            preTaxPercentiles: { p50: preTaxValue },
+            taxPaidPercentiles: { p50: taxPaid },
+            curves: { p10: values, p50: values, p90: values }
+        };
+    }
+
+    // Format currency
+    function formatCurrency(value) {
+        if (value >= 1000000) {
+            return '$' + (value / 1000000).toFixed(2) + 'M';
+        } else if (value >= 1000) {
+            return '$' + (value / 1000).toFixed(1) + 'K';
+        }
+        return '$' + value.toFixed(0);
+    }
+
+    // Chart renderer
+    const ChartRenderer = {
+        canvas: null,
+        ctx: null,
+
+        init: function(canvasId) {
+            this.canvas = document.getElementById(canvasId);
+            this.ctx = this.canvas.getContext('2d');
+            this.resize();
+        },
+
+        resize: function() {
+            const container = this.canvas.parentElement;
+            const dpr = window.devicePixelRatio || 1;
+            const rect = container.getBoundingClientRect();
+
+            this.canvas.width = rect.width * dpr;
+            this.canvas.height = 400 * dpr;
+            this.canvas.style.width = rect.width + 'px';
+            this.canvas.style.height = '400px';
+
+            this.ctx.scale(dpr, dpr);
+        },
+
+        clear: function() {
+            const width = this.canvas.width / (window.devicePixelRatio || 1);
+            const height = this.canvas.height / (window.devicePixelRatio || 1);
+            this.ctx.clearRect(0, 0, width, height);
+        },
+
+        draw: function(sp500Result, comparedResult, years, monthlyDeposit, useMonteCarlo) {
+            this.clear();
+
+            const width = this.canvas.width / (window.devicePixelRatio || 1);
+            const height = this.canvas.height / (window.devicePixelRatio || 1);
+            const padding = { top: 30, right: 100, bottom: 50, left: 80 };
+            const chartWidth = width - padding.left - padding.right;
+            const chartHeight = height - padding.top - padding.bottom;
+
+            const months = years * 12;
+            const totalDeposits = [];
+            for (let m = 0; m <= months; m++) {
+                totalDeposits.push(monthlyDeposit * m);
+            }
+
+            // Find max value for Y axis
+            let maxVal = 0;
+            const allCurves = [
+                sp500Result.curves.p90,
+                comparedResult.curves.p90,
+                totalDeposits
+            ];
+            for (const curve of allCurves) {
+                for (const val of curve) {
+                    if (val > maxVal) maxVal = val;
+                }
+            }
+            maxVal *= 1.1; // Add 10% padding
+
+            // Get computed styles for colors
+            const style = getComputedStyle(document.documentElement);
+            const textColor = style.getPropertyValue('--text-color').trim() || '#D4D4D4';
+            const dividerColor = style.getPropertyValue('--divider-color').trim() || '#4a4a4a';
+            const primaryColor = style.getPropertyValue('--primary-color').trim() || '#91e0ee';
+
+            // Draw grid
+            this.ctx.strokeStyle = dividerColor;
+            this.ctx.lineWidth = 0.5;
+            this.ctx.setLineDash([5, 5]);
+
+            // Y-axis grid lines
+            const numYLines = 5;
+            for (let i = 0; i <= numYLines; i++) {
+                const y = padding.top + (chartHeight / numYLines) * i;
+                this.ctx.beginPath();
+                this.ctx.moveTo(padding.left, y);
+                this.ctx.lineTo(width - padding.right, y);
+                this.ctx.stroke();
+            }
+
+            // X-axis grid lines
+            for (let yr = 0; yr <= years; yr++) {
+                const x = padding.left + (chartWidth / years) * yr;
+                this.ctx.beginPath();
+                this.ctx.moveTo(x, padding.top);
+                this.ctx.lineTo(x, height - padding.bottom);
+                this.ctx.stroke();
+            }
+
+            this.ctx.setLineDash([]);
+
+            // Helper to map data to canvas coordinates
+            const mapX = (month) => padding.left + (month / months) * chartWidth;
+            const mapY = (value) => padding.top + chartHeight - (value / maxVal) * chartHeight;
+
+            // Draw confidence bands if Monte Carlo
+            if (useMonteCarlo) {
+                // S&P 500 band (green)
+                this.ctx.fillStyle = 'rgba(76, 175, 80, 0.15)';
+                this.ctx.beginPath();
+                this.ctx.moveTo(mapX(0), mapY(sp500Result.curves.p10[0]));
+                for (let m = 0; m <= months; m++) {
+                    this.ctx.lineTo(mapX(m), mapY(sp500Result.curves.p90[m]));
+                }
+                for (let m = months; m >= 0; m--) {
+                    this.ctx.lineTo(mapX(m), mapY(sp500Result.curves.p10[m]));
+                }
+                this.ctx.closePath();
+                this.ctx.fill();
+
+                // Compared fund band (blue)
+                this.ctx.fillStyle = 'rgba(33, 150, 243, 0.15)';
+                this.ctx.beginPath();
+                this.ctx.moveTo(mapX(0), mapY(comparedResult.curves.p10[0]));
+                for (let m = 0; m <= months; m++) {
+                    this.ctx.lineTo(mapX(m), mapY(comparedResult.curves.p90[m]));
+                }
+                for (let m = months; m >= 0; m--) {
+                    this.ctx.lineTo(mapX(m), mapY(comparedResult.curves.p10[m]));
+                }
+                this.ctx.closePath();
+                this.ctx.fill();
+            }
+
+            // Draw total deposits line (dashed gray)
+            this.ctx.strokeStyle = '#888888';
+            this.ctx.lineWidth = 2;
+            this.ctx.setLineDash([8, 4]);
+            this.ctx.beginPath();
+            this.ctx.moveTo(mapX(0), mapY(totalDeposits[0]));
+            for (let m = 1; m <= months; m++) {
+                this.ctx.lineTo(mapX(m), mapY(totalDeposits[m]));
+            }
+            this.ctx.stroke();
+            this.ctx.setLineDash([]);
+
+            // Draw S&P 500 median line (green)
+            this.ctx.strokeStyle = '#4CAF50';
+            this.ctx.lineWidth = 2.5;
+            this.ctx.beginPath();
+            this.ctx.moveTo(mapX(0), mapY(sp500Result.curves.p50[0]));
+            for (let m = 1; m <= months; m++) {
+                this.ctx.lineTo(mapX(m), mapY(sp500Result.curves.p50[m]));
+            }
+            this.ctx.stroke();
+
+            // Draw compared fund median line (blue)
+            this.ctx.strokeStyle = '#2196F3';
+            this.ctx.lineWidth = 2.5;
+            this.ctx.beginPath();
+            this.ctx.moveTo(mapX(0), mapY(comparedResult.curves.p50[0]));
+            for (let m = 1; m <= months; m++) {
+                this.ctx.lineTo(mapX(m), mapY(comparedResult.curves.p50[m]));
+            }
+            this.ctx.stroke();
+
+            // Draw capital gains tax loss on compared fund (red segment)
+            const taxPaid = comparedResult.taxPaidPercentiles.p50;
+            const preTaxValue = comparedResult.preTaxPercentiles.p50;
+            const postTaxValue = comparedResult.percentiles.p50;
+            const endX = mapX(months);
+
+            if (taxPaid > 0) {
+                const preTaxY = mapY(preTaxValue);
+                const postTaxY = mapY(postTaxValue);
+
+                // Draw red line from pre-tax to post-tax
+                this.ctx.strokeStyle = '#F44336';
+                this.ctx.lineWidth = 3;
+                this.ctx.beginPath();
+                this.ctx.moveTo(endX, preTaxY);
+                this.ctx.lineTo(endX, postTaxY);
+                this.ctx.stroke();
+
+                // Draw red circle at post-tax point
+                this.ctx.fillStyle = '#F44336';
+                this.ctx.beginPath();
+                this.ctx.arc(endX, postTaxY, 4, 0, Math.PI * 2);
+                this.ctx.fill();
+
+                // Label the tax loss
+                this.ctx.fillStyle = '#F44336';
+                this.ctx.font = '10px monospace';
+                this.ctx.textAlign = 'left';
+                this.ctx.textBaseline = 'middle';
+                this.ctx.fillText('-' + formatCurrency(taxPaid) + ' tax', endX + 8, (preTaxY + postTaxY) / 2);
+            }
+
+            // Draw delta annotation between funds
+            const sp500Final = sp500Result.percentiles.p50;
+            const comparedFinal = comparedResult.percentiles.p50;
+            const delta = sp500Final - comparedFinal;
+
+            // Draw delta bracket/line
+            const sp500Y = mapY(sp500Final);
+            const comparedY = mapY(comparedFinal);
+            const bracketX = endX + 6;
+
+            this.ctx.strokeStyle = textColor;
+            this.ctx.lineWidth = 1;
+            this.ctx.setLineDash([]);
+            this.ctx.beginPath();
+            // Horizontal ticks
+            this.ctx.moveTo(endX + 2, sp500Y);
+            this.ctx.lineTo(bracketX, sp500Y);
+            this.ctx.moveTo(endX + 2, comparedY);
+            this.ctx.lineTo(bracketX, comparedY);
+            // Vertical line
+            this.ctx.moveTo(bracketX, sp500Y);
+            this.ctx.lineTo(bracketX, comparedY);
+            this.ctx.stroke();
+
+            // Delta label
+            this.ctx.fillStyle = delta >= 0 ? '#4CAF50' : '#F44336';
+            this.ctx.font = '11px monospace';
+            this.ctx.textAlign = 'left';
+            this.ctx.textBaseline = 'middle';
+            const deltaLabel = 'Δ ' + (delta >= 0 ? '+' : '') + formatCurrency(delta);
+            this.ctx.fillText(deltaLabel, bracketX + 4, (sp500Y + comparedY) / 2);
+
+            // Draw axes
+            this.ctx.strokeStyle = textColor;
+            this.ctx.lineWidth = 1;
+            this.ctx.beginPath();
+            this.ctx.moveTo(padding.left, padding.top);
+            this.ctx.lineTo(padding.left, height - padding.bottom);
+            this.ctx.lineTo(width - padding.right, height - padding.bottom);
+            this.ctx.stroke();
+
+            // Y-axis labels
+            this.ctx.fillStyle = textColor;
+            this.ctx.font = '12px monospace';
+            this.ctx.textAlign = 'right';
+            this.ctx.textBaseline = 'middle';
+            for (let i = 0; i <= numYLines; i++) {
+                const value = maxVal * (1 - i / numYLines);
+                const y = padding.top + (chartHeight / numYLines) * i;
+                this.ctx.fillText(formatCurrency(value), padding.left - 10, y);
+            }
+
+            // X-axis labels
+            this.ctx.textAlign = 'center';
+            this.ctx.textBaseline = 'top';
+            for (let yr = 0; yr <= years; yr++) {
+                const x = padding.left + (chartWidth / years) * yr;
+                this.ctx.fillText(yr + 'y', x, height - padding.bottom + 10);
+            }
+
+            // Legend
+            const legendY = padding.top - 15;
+            const legendItems = [
+                { color: '#4CAF50', label: 'S&P 500' },
+                { color: '#2196F3', label: 'Compared' },
+                { color: '#888888', label: 'Deposits', dashed: true },
+                { color: '#F44336', label: 'Tax Loss' }
+            ];
+
+            let legendX = padding.left;
+            this.ctx.font = '11px monospace';
+            this.ctx.textAlign = 'left';
+            this.ctx.textBaseline = 'middle';
+
+            for (const item of legendItems) {
+                // Draw line sample
+                this.ctx.strokeStyle = item.color;
+                this.ctx.lineWidth = 2;
+                if (item.dashed) {
+                    this.ctx.setLineDash([4, 2]);
+                }
+                this.ctx.beginPath();
+                this.ctx.moveTo(legendX, legendY);
+                this.ctx.lineTo(legendX + 20, legendY);
+                this.ctx.stroke();
+                this.ctx.setLineDash([]);
+
+                // Draw label
+                this.ctx.fillStyle = textColor;
+                this.ctx.fillText(item.label, legendX + 25, legendY);
+
+                legendX += this.ctx.measureText(item.label).width + 50;
+            }
+        }
+    };
+
+    // Main calculator
+    const Calculator = {
+        form: null,
+        chartRenderer: null,
+
+        init: function() {
+            this.form = document.getElementById('fund-comparison-form');
+            this.chartRenderer = Object.create(ChartRenderer);
+            this.chartRenderer.init('fund-comparison-chart');
+
+            this.form.addEventListener('submit', (e) => {
+                e.preventDefault();
+                this.calculate();
+            });
+
+            window.addEventListener('resize', () => {
+                this.chartRenderer.resize();
+                this.calculate();
+            });
+
+            // Initial calculation
+            this.calculate();
+        },
+
+        getInputs: function() {
+            return {
+                sp500: {
+                    annualReturn: parseFloat(document.getElementById('sp500-return').value) / 100,
+                    annualVol: parseFloat(document.getElementById('sp500-volatility').value) / 100,
+                    expenseRatio: parseFloat(document.getElementById('sp500-expense').value) / 100,
+                    capitalGainsTax: 0,
+                    monthlyDeposit: parseFloat(document.getElementById('monthly-deposit').value)
+                },
+                compared: {
+                    annualReturn: parseFloat(document.getElementById('compared-return').value) / 100,
+                    annualVol: parseFloat(document.getElementById('compared-volatility').value) / 100,
+                    expenseRatio: parseFloat(document.getElementById('compared-admin-fee').value) / 100,
+                    capitalGainsTax: parseFloat(document.getElementById('compared-capital-gains').value) / 100,
+                    monthlyDeposit: parseFloat(document.getElementById('monthly-deposit').value)
+                },
+                years: parseInt(document.getElementById('time-frame').value),
+                useMonteCarlo: document.getElementById('use-monte-carlo').checked
+            };
+        },
+
+        calculate: function() {
+            const inputs = this.getInputs();
+            const months = inputs.years * 12;
+            const numSimulations = 1000;
+
+            let sp500Result, comparedResult;
+
+            if (inputs.useMonteCarlo) {
+                sp500Result = runMonteCarlo(inputs.sp500, months, numSimulations);
+                comparedResult = runMonteCarlo(inputs.compared, months, numSimulations);
+            } else {
+                sp500Result = runDeterministic(inputs.sp500, months);
+                comparedResult = runDeterministic(inputs.compared, months);
+            }
+
+            // Draw chart
+            this.chartRenderer.draw(
+                sp500Result,
+                comparedResult,
+                inputs.years,
+                inputs.sp500.monthlyDeposit,
+                inputs.useMonteCarlo
+            );
+
+            // Update summary
+            this.updateSummary(sp500Result, comparedResult, inputs);
+        },
+
+        updateSummary: function(sp500Result, comparedResult, inputs) {
+            const totalDeposits = inputs.sp500.monthlyDeposit * inputs.years * 12;
+
+            // Summary table
+            document.getElementById('total-deposits').textContent = formatCurrency(totalDeposits);
+
+            document.getElementById('sp500-final').textContent = formatCurrency(sp500Result.percentiles.p50);
+            const sp500Gain = sp500Result.percentiles.p50 - totalDeposits;
+            document.getElementById('sp500-gain').textContent = formatCurrency(sp500Gain);
+            document.getElementById('sp500-multiple').textContent = (sp500Result.percentiles.p50 / totalDeposits).toFixed(2) + 'x';
+
+            document.getElementById('compared-final').textContent = formatCurrency(comparedResult.percentiles.p50);
+            const comparedGain = comparedResult.percentiles.p50 - totalDeposits;
+            document.getElementById('compared-gain').textContent = formatCurrency(comparedGain);
+            document.getElementById('compared-multiple').textContent = (comparedResult.percentiles.p50 / totalDeposits).toFixed(2) + 'x';
+
+            // Percentiles section
+            const percentilesSection = document.getElementById('percentiles-section');
+            if (inputs.useMonteCarlo) {
+                percentilesSection.style.display = 'block';
+
+                document.getElementById('sp500-p10').textContent = formatCurrency(sp500Result.percentiles.p10);
+                document.getElementById('sp500-p25').textContent = formatCurrency(sp500Result.percentiles.p25);
+                document.getElementById('sp500-p50').textContent = formatCurrency(sp500Result.percentiles.p50);
+                document.getElementById('sp500-p75').textContent = formatCurrency(sp500Result.percentiles.p75);
+                document.getElementById('sp500-p90').textContent = formatCurrency(sp500Result.percentiles.p90);
+
+                document.getElementById('compared-p10').textContent = formatCurrency(comparedResult.percentiles.p10);
+                document.getElementById('compared-p25').textContent = formatCurrency(comparedResult.percentiles.p25);
+                document.getElementById('compared-p50').textContent = formatCurrency(comparedResult.percentiles.p50);
+                document.getElementById('compared-p75').textContent = formatCurrency(comparedResult.percentiles.p75);
+                document.getElementById('compared-p90').textContent = formatCurrency(comparedResult.percentiles.p90);
+            } else {
+                percentilesSection.style.display = 'none';
+            }
+        }
+    };
+
+    // Initialize on DOM ready
+    if (document.readyState === 'loading') {
+        document.addEventListener('DOMContentLoaded', () => Calculator.init());
+    } else {
+        Calculator.init();
+    }
+})();
diff --git a/templates/shortcodes/fund_comparison.html b/templates/shortcodes/fund_comparison.html
new file mode 100644
index 0000000..fe9e1cf
--- /dev/null
+++ b/templates/shortcodes/fund_comparison.html
@@ -0,0 +1,146 @@
+<div class="fund-comparison-container">
+    <noscript>
+        <div class="noscript-warning">
+            This calculator requires JavaScript to function.
+        </div>
+    </noscript>
+
+    <form id="fund-comparison-form" class="fund-comparison-form">
+        <div class="form-section">
+            <h3>S&P 500 Index Fund</h3>
+            <div class="form-group">
+                <label for="sp500-return">Expected yearly return (%)</label>
+                <input type="number" id="sp500-return" value="10" step="0.1" required>
+            </div>
+            <div class="form-group">
+                <label for="sp500-volatility">Volatility / std dev (%)</label>
+                <input type="number" id="sp500-volatility" value="15" step="0.1" required>
+            </div>
+            <div class="form-group">
+                <label for="sp500-expense">Expense ratio (%)</label>
+                <input type="number" id="sp500-expense" value="0.03" step="0.01" required>
+            </div>
+        </div>
+
+        <div class="form-section">
+            <h3>Compared Fund</h3>
+            <div class="form-group">
+                <label for="compared-return">Expected yearly return (%)</label>
+                <input type="number" id="compared-return" value="7" step="0.1" required>
+            </div>
+            <div class="form-group">
+                <label for="compared-volatility">Volatility / std dev (%)</label>
+                <input type="number" id="compared-volatility" value="10" step="0.1" required>
+            </div>
+            <div class="form-group">
+                <label for="compared-admin-fee">Admin fee (% yearly)</label>
+                <input type="number" id="compared-admin-fee" value="1" step="0.01">
+            </div>
+            <div class="form-group">
+                <label for="compared-capital-gains">Capital gains tax at withdrawal (%)</label>
+                <input type="number" id="compared-capital-gains" value="0" step="0.1">
+            </div>
+        </div>
+
+        <div class="form-section form-section-full">
+            <h3>Investment Parameters</h3>
+            <div class="form-row">
+                <div class="form-group">
+                    <label for="time-frame">Time frame (years)</label>
+                    <input type="number" id="time-frame" value="20" min="1" max="50" required>
+                </div>
+                <div class="form-group">
+                    <label for="monthly-deposit">Monthly deposit ($)</label>
+                    <input type="number" id="monthly-deposit" value="500" min="1" required>
+                </div>
+            </div>
+            <div class="checkbox-group">
+                <input type="checkbox" id="use-monte-carlo" checked>
+                <label for="use-monte-carlo">Use Monte Carlo simulation (1000 runs)</label>
+            </div>
+            <button type="submit" class="calculate-btn">Calculate</button>
+        </div>
+    </form>
+
+    <div class="chart-container">
+        <canvas id="fund-comparison-chart"></canvas>
+    </div>
+
+    <div class="summary-section">
+        <h3>Summary</h3>
+        <table class="summary-table">
+            <thead>
+                <tr>
+                    <th></th>
+                    <th>S&P 500 Fund</th>
+                    <th>Compared Fund</th>
+                </tr>
+            </thead>
+            <tbody>
+                <tr>
+                    <td>Total Deposits</td>
+                    <td colspan="2" id="total-deposits">-</td>
+                </tr>
+                <tr>
+                    <td>Final Value (median)</td>
+                    <td id="sp500-final">-</td>
+                    <td id="compared-final">-</td>
+                </tr>
+                <tr>
+                    <td>Total Gain</td>
+                    <td id="sp500-gain">-</td>
+                    <td id="compared-gain">-</td>
+                </tr>
+                <tr>
+                    <td>Return Multiple</td>
+                    <td id="sp500-multiple">-</td>
+                    <td id="compared-multiple">-</td>
+                </tr>
+            </tbody>
+        </table>
+    </div>
+
+    <div id="percentiles-section" class="summary-section">
+        <details class="percentiles-details">
+            <summary>Percentile Breakdown</summary>
+            <table class="summary-table percentiles-table">
+                <thead>
+                    <tr>
+                        <th>Percentile</th>
+                        <th>S&P 500 Fund</th>
+                        <th>Compared Fund</th>
+                    </tr>
+                </thead>
+                <tbody>
+                    <tr>
+                        <td>10th (pessimistic)</td>
+                        <td id="sp500-p10">-</td>
+                        <td id="compared-p10">-</td>
+                    </tr>
+                    <tr>
+                        <td>25th</td>
+                        <td id="sp500-p25">-</td>
+                        <td id="compared-p25">-</td>
+                    </tr>
+                    <tr>
+                        <td>50th (median)</td>
+                        <td id="sp500-p50">-</td>
+                        <td id="compared-p50">-</td>
+                    </tr>
+                    <tr>
+                        <td>75th</td>
+                        <td id="sp500-p75">-</td>
+                        <td id="compared-p75">-</td>
+                    </tr>
+                    <tr>
+                        <td>90th (optimistic)</td>
+                        <td id="sp500-p90">-</td>
+                        <td id="compared-p90">-</td>
+                    </tr>
+                </tbody>
+            </table>
+        </details>
+    </div>
+</div>
+
+<script src="{{ get_url(path='js/fundComparison.js') | safe }}"></script>