# FIRE Calculator - 4% Rule, Monte Carlo & Coast FI

> Find your FIRE number and years to financial independence from income, spending and real returns, with Monte Carlo success rates, Coast FI and Barista FI.

- URL: https://qilingtools.com/en/math/fire
- Category: Math Tools (https://qilingtools.com/en/math)
- Tags: [Math](https://qilingtools.com/en/tags/math), [Finance](https://qilingtools.com/en/tags/finance)
- Last updated: 2026-10-26
- Price: Free, no sign-up
- Privacy: Runs locally in the browser; files are never uploaded

FIRE — financial independence, retire early — comes down to two numbers: what you spend each year and how much you need invested to live off it. Enter your age, invested assets, after-tax income and spending (or drag the savings-rate slider), set the real return after inflation and the withdrawal rate, and the tool computes your FIRE number as spending ÷ withdrawal rate (25× spending under the 4% rule), solves the future-value equation in closed form for the years until you get there and your FI age, and projects the portfolio year by year through accumulation and retirement. Markets don’t move in a straight line, so there’s a Monte Carlo simulation too: each year’s return is lognormal with your expected return as the mean and your volatility as the SD, thousands of reproducible paths (the same seed always gives the same result) are drawn as 10–90% and 25–75% percentile bands, and the success rate counts the paths that don’t run out of money before your planning age — sequence-of-returns risk made visible. Two variants are included: Coast FI is how much you need today so that, with no further contributions, compounding alone reaches the FIRE number by your target age; Barista FI is the smaller target when part-time income still covers some spending. A sensitivity table crosses returns with savings rates, showing why saving more usually beats chasing returns. Amounts are in today’s money with an option to show nominal values, and the currency symbol switches between ¥ and $. For education and rough planning only, not financial advice.

## How to use

1. Enter your age, invested assets, after-tax income and spending (or use the savings-rate slider)
2. Set the real return, inflation and withdrawal rate, plus volatility and the number of simulations
3. Read the FIRE number, years to FI, success rate, projection chart, Coast/Barista FI and sensitivity table

## Features

- FIRE number and years to FI (closed-form)
- Year-by-year projection with a detail table
- Seeded Monte Carlo with percentile bands and success rate
- Coast FI: the balance that grows to your target on its own
- Barista FI: the target with part-time income
- Return × savings-rate sensitivity table
- Today’s money or nominal, ¥ or $
- Transparent formulas, computed locally in your browser

## FAQ

### What is the 4% rule?

It comes from the 1998 Trinity study: withdraw 4% of your portfolio in the first year of retirement and adjust that amount for inflation each year, and a stock–bond portfolio survived most historical 30-year periods. Turned around, your FIRE number is 25× annual spending. Early retirees may need the money to last 40–60 years, so many use a more conservative 3–3.5%; you can change the rate here.

### Why use real rather than nominal returns?

The real return is roughly the nominal return minus inflation. Working in real terms keeps every amount in today’s money, so the FIRE number stays meaningful — 7% nominal with 2% inflation is about 5% real. Tick “show nominal amounts” to see the inflated figures you’d actually see on your statements.

### How should I read the Monte Carlo success rate?

It’s the share of simulated paths, under random returns, that retire on schedule and don’t run out of money before your planning age. Even with the same average return, paths that hit a bear market right after retirement fail more often — that’s sequence-of-returns risk. Above 90% is usually considered robust; below 75%, consider spending less, retiring later or keeping some part-time income.

### What’s the difference between Coast FI and Barista FI?

Coast FI means you already have enough that, with no further contributions, compounding alone reaches your FIRE number by your target retirement age (say 60); from then on you only need to earn your current spending. Barista FI means keeping some part-time income in retirement, so the portfolio only covers the rest: (spending − part-time income) ÷ withdrawal rate, a much nearer target.

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