Finance & Property · Introduction
Compound Interest & FIRE Calculator
Compare compounding, purchasing power, retirement withdrawals and FIRE scenarios.
Updated 2026-10-25 · ThinkVault Tools
What can this tool help you do?
Compare compounding, purchasing power, retirement withdrawals and FIRE scenarios.
Check the purpose and assumptions, then open the tool. Return to the guide for details.
Purpose and inputs
Purpose and inputs
Compare monthly or annual compounding, real purchasing power, retirement withdrawals and time to a FIRE target.
Method and assumptions
Each period earns interest before the deposit: new balance = old balance × (1+r/n) + monthly deposit×12/n; n is 12 or 1. Annual mode credits the year’s deposits at year-end. Real value = nominal/(1+inflation)^years; monthly retirement income = nominal×withdrawal rate/12. FIRE target = today’s monthly spending×12/withdrawal rate, tested against real assets at year-end up to 100 years. The default 4% is a scenario, not a guarantee.
Method
Each period earns interest before the deposit: new balance = old balance × (1+r/n) + monthly deposit×12/n; n is 12 or 1. Annual mode credits the year’s deposits at year-end. Real value = nominal/(1+inflation)^years; monthly retirement income = nominal×withdrawal rate/12. FIRE target = today’s monthly spending×12/withdrawal rate, tested against real assets at year-end up to 100 years. The default 4% is a scenario, not a guarantee.
Before you begin
Tax, lending, holiday and protection rules vary by place and date. Check current local rules and provider terms. Results are estimates.