Finance & Property · How to use
Compound Interest & FIRE Calculator
Follow the steps to enter your numbers and check the limits.
Updated 2026-10-25 · ThinkVault Tools
Get started in three steps
- 1
Step 1
Prepare your amounts, terms and applicable rates or prices.
- 2
Step 2
Open the tool, check the units and compare scenarios.
- 3
Step 3
Read the results and notes. Check official documents and sources before deciding.
Method and common questions
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.
FAQ
- What are the limitations?
- Annual mode credits the year’s deposits at year-end. FIRE compares real assets with today’s spending; 4% is not guaranteed.
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.
Investor.gov compound interestLast checked: 2026-10-19
Before you begin
Tax, lending, holiday and protection rules vary by place and date. Check current local rules and provider terms. Results are estimates.