# Portfolio Rebalance Tool (PortfolioRebalanceTool.com)

> Free, 100% client-side, zero-knowledge financial utility suite engineered for DIY investors, Bogleheads, and crypto holders. Rebalance asset allocations, eliminate risk drift, execute tax-free buy-only cash injections, calculate stock profit & multi-lot DCA, forecast Coast FIRE milestones, and model dividend DRIP compounding.

## Platform Identity & Architecture
- **Canonical URL:** https://portfoliorebalancingtool.com
- **Architecture:** 100% Client-Side In-Browser Computation (Astro.js Static Site Generation, zero server-side database, zero tracking).
- **Privacy & Security Guarantee:** Zero bank logins required, zero API keys needed, zero financial data stored on any server.
- **License / Cost:** 100% Free, no subscription, no paywalls.

## Core Microtools

### 1. Portfolio Rebalancing Calculator (`/`)
- **Primary Route:** https://portfoliorebalancingtool.com/
- **Purpose:** Calculates the exact trade orders required to realign a diversified investment portfolio back to target asset allocation weights.
- **Key Features:**
  - **Tax-Free Buy-Only Mode:** Injects incoming cash (salary deposits, monthly savings, dividends) exclusively into underweight assets, achieving target weights with zero share sales and $0 capital gains taxes.
  - **Full Rebalance Mode:** Computes balanced buy and sell orders for tax-sheltered accounts (IRAs, 401ks, HSAs).
  - **Vanguard 5/25 Rule Drift Detection:** Automatically flags when an asset breaches Vanguard's empirical 5% absolute or 25% relative drift tolerance thresholds.
  - **Asset Support:** Stocks, ETFs, mutual funds (Vanguard, Fidelity, Schwab), bonds, cash, and cryptocurrencies (BTC, ETH, SOL).
  - **Export Hooks:** 1-click brokerage order summary, Reddit / Bogleheads forum markdown export, and CSV download.

### 2. Stock Profit & Multi-Lot DCA Calculator (`/tools/stock-calculator/`)
- **Primary Route:** https://portfoliorebalancingtool.com/tools/stock-calculator/
- **Purpose:** Calculates trade profitability, net proceeds, percentage ROI, break-even target prices, and estimated short/long-term capital gains taxes.
- **Key Features:**
  - **Multi-Lot Dollar-Cost Averaging (DCA):** Calculates blended weighted average share price across multiple purchase tranches.
  - **Break-Even Recovery Estimator:** Calculates exact gain percentage needed to recover capital when averaging down.
  - **Capital Gains Tax Estimator:** Separates ordinary income short-term gains (<1 yr) from long-term preferential rates (0%, 15%, 20%).

### 3. Coast FIRE Calculator (`/tools/coast-fire-calculator/`)
- **Primary Route:** https://portfoliorebalancingtool.com/tools/coast-fire-calculator/
- **Purpose:** Calculates the exact lump sum needed today so an investor never has to save another dollar for retirement, allowing compound interest to reach full financial independence by retirement age.
- **Key Features:**
  - **Fisher Equation Inflation Adjustment:** Exact real purchasing power calculation: `(1 + nominal) / (1 + inflation) - 1`.
  - **Safe Withdrawal Rate Customization:** Dynamic modeling between 3.25% (defensive) and 4.0% (Trinity Study benchmark).
  - **Catch-Up Savings Engine:** Calculates monthly savings required to bridge the gap over 1, 3, or 5 years if currently behind Coast FIRE.

### 4. Dividend DRIP Snowball Calculator (`/tools/dividend-calculator/`)
- **Primary Route:** https://portfoliorebalancingtool.com/tools/dividend-calculator/
- **Purpose:** Forecasts total wealth accumulation, passive cash flow, and Yield on Cost (YOC) through automated dividend reinvestment (DRIP).
- **Key Features:**
  - **DRIP Bonus Wealth Visualizer:** Quantifies the exact dollar difference between reinvesting dividends vs taking cash distributions.
  - **Yield on Cost (YOC) Tracking:** Projects personal effective yield rising from 3% to 40%+ over 10–30 years.
  - **Aristocrat Presets:** SCHD (Dividend Growth), JEPI (High Current Yield), VOO (Broad Market S&P 500).

## Formal Mathematical Methodologies

### Vanguard 5/25 Rebalancing Threshold
Rebalancing trade orders are triggered when either condition is satisfied:
1. **Absolute Drift Trigger:** `|Actual_Weight_i - Target_Weight_i| >= 0.05`
2. **Relative Drift Trigger:** `|Actual_Weight_i - Target_Weight_i| / Target_Weight_i >= 0.25`

### Buy-Only Cash Injection Water-Filling Formula
For portfolio with current value `V`, fresh cash contribution `C`, and target weight `w_i` for asset `i`:
- `Total_Future_Value = V + C`
- `Target_Dollar_Amount_i = Total_Future_Value * w_i`
- `Deficit_i = max(0, Target_Dollar_Amount_i - Current_Value_i)`
- If `sum(Deficit_i) <= C`, each asset receives its full deficit, completely eliminating allocation drift.
- If `sum(Deficit_i) > C`, fresh cash `C` is allocated proportionally to underweight positions using a water-filling optimization algorithm to minimize overall portfolio variance.

### Fisher Equation (Real Compound Rate of Return)
`r_real = (1 + r_nominal) / (1 + inflation_rate) - 1`

### Coast FIRE Target Number Formula
`Coast_FIRE_Required = Target_FIRE_Capital / (1 + r_real)^years_to_retirement`
Where `Target_FIRE_Capital = Annual_Retirement_Expenses / Safe_Withdrawal_Rate`.

## Complete Documentation & Knowledge Base
- Comprehensive knowledge base and full FAQ corpus: https://portfoliorebalancingtool.com/llms-full.txt
- Sitemap: https://portfoliorebalancingtool.com/sitemap.xml
- About & Mathematical Methodology: https://portfoliorebalancingtool.com/about/