FIRE

Project intro

FIRE is a day-by-day financial independence simulator built in Python. It answers one question: how many years at a high salary do you need before you can stop working, coast on a job that covers your core expenses until 60, or retire without your nest egg ever shrinking? The simulator models your money day by day all the way to age 112, in today's dollars. Each day wages arrive net of income tax, expenses go out padded by a 1.1x safety factor, and any surplus is invested; shortfalls are covered by selling from the portfolio and paying tax on the sale. A bisection solver then finds the shortest high-salary stretch that keeps the balance above $0 every single day. Each plan is solved for three goals: retire to $0 (money lasts to 112), coast until 60, and retire with a portfolio that never shrinks after 100. Output includes the stop age to the day and the portfolio at that age, an income-plan table, terminal charts for net worth, expenses by category and cash flow, what-if tables showing how many weeks sooner you could stop with extra savings at a given age, and grid sweeps across plans, income ladders, partner incomes and tax setups in one table. It ships with 401(k), Roth and 529 accounts on by default, 2026 federal and 2025 California bracket tables, and shipped examples: an SF family on a 120 → 175 → 230k ladder, an Austin variant with Texas taxes, and a move-cities scenario that switches expenses and taxes at age 35. Plans are plain Python files, so you can describe your life in plain English and have an AI assistant write your plan. The author states up front that this is a vibe-coded tool: someone described what they wanted, and Claude wrote the code, the tests and the design log. The repo ships a pytest suite and a DESIGN.md design log documenting the decisions. The README also carries a clear disclaimer: no financial professional has reviewed it — it is not financial advice, and anything important should be checked with a real human.