FIRE Calculator

A comprehensive Financial Independence, Retire Early (FIRE) calculator built as a single-page web application. Input your financial data and get detailed projections for when you can achieve financial independence, complete with interactive charts, Monte Carlo simulations, and what-if scenario analysis.

Features

Core Calculator

• FIRE Number Calculation — Computes your target portfolio using the safe withdrawal rate (SWR) method with gap-and-residual modeling for pension integration
• Year-by-Year Projections — Full accumulation and drawdown simulation from current age to life expectancy
• Three FIRE Types — Lean, Regular, and Fat FIRE with configurable post-retirement spending percentages
• Coast FIRE & Barista FIRE — Additional FIRE milestone calculations
• Bridge Strategy — Models future income events (inheritance, severance) that can bring your FIRE date forward

Financial Modeling

• Pension Integration — Gap-year model accounts for pre-pension and post-pension phases separately
• Flexible Asset Modeling — Invested assets, cash savings, custom assets (per-asset return/contribution), and real estate cash-flow/appreciation
• Debt Tracking — Multiple debts with monthly payments and remaining years, factored into projections
• Life Events — Planned future expenses (house purchase, wedding) and income (inheritance) with timeline
• Capital Gains Tax — Applied to investment returns
• Annual Fees (TER) — Investment fund fees subtracted from gross returns
• Inflation Adjustment — Toggle between nominal and real (inflation-adjusted) values
• Salary Growth — Annual salary growth rate modeling

Monte Carlo Simulation

• 500 Randomized Scenarios — Uses a seeded PRNG (Mulberry32) for deterministic, reproducible results
• Percentile Bands — P10, P25, P50 (median), P75, P90 portfolio projections
• Success Rate — Percentage of simulations where portfolio lasts through retirement
• FIRE Age Distribution — Histogram of when FIRE is achieved across simulations
• Target Age Mode — Force a specific retirement age and see survival probability

Visualizations

• Net Worth Projection Chart — Portfolio growth with optimistic/pessimistic bands and FIRE target line
• Monte Carlo Chart — Percentile fan chart across all simulations
• Income vs Expenses Chart — Stacked area showing income sources vs spending over time
• Post-Retirement Withdrawal Chart — Drawdown phase with pension overlay
• Wealth Breakdown Chart — Contributions vs investment growth at FIRE
• Milestone Timeline — Visual progress toward Emergency Fund, 100k, Coast FIRE, Half FIRE, and FIRE

What-If Scenarios

• Side-by-Side Comparison — Adjust investment amount, return rate, expenses, or SWR and see impact
• Difference Indicators — Shows how many years sooner/later each scenario reaches FIRE

User Experience

• Multi-Currency — 15 supported currencies (EUR, USD, GBP, CHF, JPY, CAD, AUD, NZD, CNY, HKD, SGD, INR, SEK, NOK, DKK) with locale-aware formatting
• Internationalization — Full English and Italian translations
• Dark/Light Theme — System preference detection with manual override
• Shareable URLs — Encode all inputs in a URL hash for sharing
• Profile Manager — Save and load multiple financial profiles to localStorage
• Responsive Design — Works on desktop and mobile with sticky input panel
• Expense Breakdown — Detailed category-level expense tracking (housing, food, transport, etc.)

Tech Stack

Category	Technology
Framework	React 19 + TypeScript 5.6
Build	Vite 6
Styling	Tailwind CSS 3.4 with CSS custom properties
State	Zustand 5 with persist middleware
Charts	Recharts 2
Animations	Framer Motion 11
Icons	Lucide React
Testing	Vitest 4

Getting Started

Prerequisites

• Node.js 18+
• npm, yarn, or pnpm

Installation

# Clone the repository
git clone https://github.com/your-username/fire-calculator.git
cd fire-calculator

# Install dependencies
npm install

# Start development server
npm run dev

The app will be available at http://localhost:5173.

Available Scripts

Command	Description
npm run dev	Start development server with HMR
npm run build	Type-check and build for production
npm run preview	Preview the production build locally
npm run test	Run all tests once
npm run test:watch	Run tests in watch mode

Project Structure

src/
├── components/
│   ├── layout/
│   │   ├── Header.tsx          # App header with theme/language/currency controls
│   │   ├── InputPanel.tsx      # All financial input forms
│   │   └── ProfileManager.tsx  # Save/load profile management
│   ├── results/
│   │   ├── BreakdownChart.tsx      # Contributions vs growth pie chart
│   │   ├── IncomeExpenseChart.tsx   # Income vs expenses over time
│   │   ├── MilestoneTimeline.tsx    # Visual milestone progress
│   │   ├── MonteCarloChart.tsx      # Monte Carlo percentile fan chart
│   │   ├── ProjectionChart.tsx      # Net worth projection chart
│   │   ├── ResultsDashboard.tsx     # Main results layout
│   │   ├── ScenarioComparison.tsx   # What-if scenario table
│   │   ├── SummaryCards.tsx         # Key metric summary cards
│   │   └── WithdrawalChart.tsx      # Post-retirement drawdown chart
│   ├── shared/
│   │   └── FormFields.tsx      # Reusable currency/percent/number inputs
│   └── ui/                     # Base UI primitives (Button, Card, Input, etc.)
├── lib/
│   ├── calculator.ts           # Core FIRE calculation engine
│   ├── constants.ts            # Default values and configuration
│   ├── financial.ts            # Shared financial math (annuity PV, drawdown)
│   ├── formatters.ts           # Currency, percent, date formatting
│   ├── monteCarlo.ts           # Monte Carlo simulation engine
│   ├── sharing.ts              # URL hash encoding/decoding
│   ├── utils.ts                # Tailwind class merging utility
│   └── i18n/                   # Internationalization
│       ├── en.ts               # English translations
│       ├── it.ts               # Italian translations
│       ├── index.ts            # i18n context and hooks
│       └── types.ts            # Translation type definitions
├── store/
│   ├── fireStore.ts            # Zustand store for financial inputs + computed results
│   └── uiStore.ts              # Zustand store for theme/locale/currency + UI preferences
├── test/
│   ├── setup.ts                # Test setup (jest-dom matchers)
│   ├── calculator.test.ts      # Calculator engine tests
│   ├── financial.test.ts       # Financial math unit tests
│   ├── formatters.test.ts      # Formatter utility tests
│   ├── monteCarlo.test.ts      # Monte Carlo simulation tests
│   └── sharing.test.ts         # URL sharing round-trip tests
└── types/
    └── index.ts                # TypeScript type definitions

How It Works

FIRE Number Calculation

The calculator uses the Safe Withdrawal Rate (SWR) method as its foundation:

$$\text{FIRE Number (base)} = \frac{\text{Annual Expenses} \times \text{Post-Retirement Factor}}{\text{SWR}}$$

This is then adjusted for:

1. Pension Credit — If you have a state/private pension, the portfolio only needs to cover the shortfall between expenses and pension income. Pre-pension "gap years" are modeled as an annuity.

2. Debt Cost — Present value of remaining debt payments at the projected FIRE age is added to the target.

3. Inflation — The final FIRE number is inflated to nominal terms at the projected FIRE age.

Portfolio Projection

Each year in the simulation:

• Accumulation Phase: Portfolio += Growth + Monthly Investment × 12 + Net One-Time Events
• Drawdown Phase: Portfolio += Growth − Withdrawals + Pension + Net One-Time Events

Net return accounts for both capital gains tax and fund fees (TER):

$$\text{Net Return} = (\text{Gross Return} - \text{Annual Fees}) \times (1 - \text{Capital Gains Tax Rate})$$

Monte Carlo Method

The simulation runs 500 paths with randomized annual returns drawn from a normal distribution:

$$R_{\text{year}} = \mu + \sigma \cdot Z$$

Where $\mu$ is the expected net return, $\sigma = 0.12$ (diversified portfolio volatility), and $Z$ is a standard normal variate. A seeded PRNG ensures identical inputs always produce identical results.

Adding a New Language

1. Create a new file in src/lib/i18n/ (e.g., de.ts) implementing the Translations interface
2. Add the locale to the Locale type in src/lib/i18n/types.ts
3. Register the translations in src/lib/i18n/index.ts
4. Add the locale option to the language selector in src/components/layout/Header.tsx

TypeScript will enforce that all translation keys are provided — the project won't compile with missing translations.

Running in a Container

You can build and run this application locally as a container using Podman or Docker. The container uses a multi-stage build: Node.js compiles the app, then the static output is served by a minimal Chainguard nginx image (distroless, non-root, zero known CVEs at the time of writing).

Prerequisites

• Podman or Docker

Scripts

Script	Description
./container-build.sh	Build the container image
./container-run.sh	Run the container (default port 18080)
./container-smoke-test.sh	Run smoke tests against the running container (assumes default port 18080)
./container-delete.sh	Stop and remove the container image from your local image repository (freeing up space)

Quick Start

./container-build.sh
./container-run.sh

Open http://127.0.0.1:18080 in your browser. Press Ctrl+C to stop.

All scripts auto-detect Podman or Docker (preferring Podman). The run and smoke test scripts accept a custom port as an argument:

./container-run.sh 12345          # run on port 12345
./container-smoke-test.sh 12345   # test on port 12345

Clean Up

To stop the container (if it is still running) and remove the container image, run the following command:

./container-delete.sh

Disclaimer

This calculator is for educational and planning purposes only. It does not constitute financial advice. The projections are based on simplified models and assumptions (constant real returns, fixed inflation, etc.) that may not reflect actual market conditions. Always consult a qualified financial advisor for personal financial decisions.

Contributors

Thanks to everyone who contributed to this project.

• vzamb — Project maintainer
• brandonp20 — Custom assets support
• benwilcock - Docker support

License

This project is licensed under the MIT License.