How to Use the FIRE Number & Coast FIRE Calculator

This free calculator estimates the portfolio that would fund your retirement spending (your FIRE number), the smaller amount you need today so compounding can finish the job (your Coast FIRE number), how many years until full financial independence if you keep contributing, and the age at which you can stop adding new money.

FIRE vs Coast FIRE

FIRE number: the nest egg that supports your planned annual spending at a chosen safe withdrawal rate. At 4%, that is 25× spending.
Full FIRE / years to independence: the point where your portfolio, including ongoing contributions, first reaches that nest egg. You could stop working from investment income alone.
Coast FIRE: the earlier point where the portfolio is already large enough that, with zero further contributions, compound growth is projected to reach the FIRE number by your target retirement age. You keep covering living costs from work, but retirement saving is no longer required.

Step-by-Step Guide

1. Enter Your Plan

Currency: choose the currency for every figure on the page.
Current age and target retirement age: the runway compounding has to work if you later stop contributing.
Current invested portfolio: money already invested toward FI.
Monthly contribution: new money you plan to add while you are still saving.
Annual retirement spending: the lifestyle you want investments to fund, in today’s money.
Safe withdrawal rate: 4% is the common Trinity Study starting point; a lower rate means a larger FIRE number.
Expected real return: growth after inflation. 7% is a long-run equity-heavy rule of thumb; 5–6% is more conservative.
Inflation (optional): leave at 0% to treat the return as real. If you enter inflation, the return field is treated as nominal and the calculator converts it to a real rate so results stay in today’s money.
Saved inputs: values are stored in this browser and restored on your next visit. Use Clear saved inputs to return to defaults.

2. How the Numbers Are Calculated

FIRE = Annual spending ÷ SWR

Coast today = FIRE ÷ (1 + r)ⁿ

Here r is the real annual return and n is target retirement age minus current age. The year-by-year table and chart then grow the portfolio monthly: contributions are added each month (on the “keep saving” path only) and the balance is compounded at the equivalent monthly real rate.

3. Read the Results

FIRE number: the full FI target in today’s money.
Coast FIRE number (today): what you would need invested right now to stop contributing immediately and still hit FIRE by the target age.
Years to independence / age at full FIRE: when continued contributions are projected to reach the FIRE number. This may be after your target age — the calculator still reports it.
Coast age: the first age at which the “keep saving” balance is at or above that year’s Coast threshold. After that age you can set contributions to zero and still be projected to arrive on time.
Gap to Coast today: how much more you need invested now to be already coasting, plus a progress percentage.

4. Read the Chart and Table

The indigo line is your portfolio if you keep contributing.
The dashed green line is the same starting balance with no further contributions.
The amber line is the Coast threshold at each age — it rises toward the FIRE number as retirement approaches, because less time remains for compounding.
The red line is the FIRE number. You are Coast FIRE when indigo crosses amber, and fully FI when indigo crosses red.

Common Scenarios & Examples

Scenario: Default plan (modest saver)

Goal: See the FIRE number, today’s Coast number, and whether $500 a month reaches independence by 65.

Leave the defaults: age 35, retire at 65, portfolio $50,000, monthly $500.
Annual retirement spending $40,000, SWR 4%, real return 7%, inflation 0%.
Watch the Results panel, chart, and table update live.

Sample inputs:

FIRE number = $40,000 ÷ 4% = $1,000,000
Years of runway n = 65 − 35 = 30
Coast today ≈ $1,000,000 ÷ 1.07³⁰ ≈ $131,000

You start about 38% of the way to Coast. At $500/month the portfolio is projected near $969,000 at 65 — just short of FIRE — and crosses $1,000,000 around age 66. Coast age and full FIRE land together in this modest-saving case.

Scenario: Stop contributing years before retirement

Goal: Raise monthly saving until Coast FIRE arrives well before the target age.

Keep the same ages, portfolio, spending, SWR and 7% real return.
Increase Monthly Contribution to $1,500.
Compare Coast age with age at full FIRE.

What changes:

With $1,500/month, Coast FIRE typically arrives in the early 40s. From that age you could contribute $0 and still be projected to reach $1,000,000 by 65. Full FIRE (the point you could stop working entirely) still comes later — around the mid-50s — because the portfolio has to grow all the way to the FIRE number, not just to the discounted Coast threshold.

Scenario: Already coasting

Goal: Test whether a larger current portfolio already lets you stop contributing.

Set Current Invested Portfolio to $150,000 and Monthly Contribution to 0.
Leave the other defaults.

Why this works:

$150,000 is already above the ~$131,000 Coast number today. Status should read that you can stop contributing now. The green “stop today” line and the indigo “keep saving” line will match if monthly contributions are zero, and both are projected to reach the FIRE line by 65 at 7% real.

Disclaimer & Limitations

Not professional advice: this calculator is an estimation and educational tool. It is not financial, tax or investment advice. Actual returns vary and past performance does not guarantee future results. Speak to a qualified adviser about your own situation.

Assumptions: a constant real rate of return, regular monthly contributions at the start of each month on the saving path, no fees, no taxes, and no pensions or state benefits unless you reduce spending to model them yourself. Safe withdrawal rates (including the 4% / Trinity rule of thumb) are historical guidelines, not guarantees. Sequence-of-returns risk, spending changes and longevity can all move the real outcome.

Today’s money: when inflation is 0%, the return is treated as real so every figure is in today’s currency. If you enter inflation, the calculator converts nominal return to a real rate with (1 + nominal) ÷ (1 + inflation) − 1. The published Coast formula uses annual compounding; the table and chart use monthly compounding so they stay consistent with the suite’s compound-growth tool. Small differences between the closed-form Coast number and the simulated path are expected.

After the target age: if contributions do not reach the FIRE number by your target retirement age, the calculator still reports the later age at which independence is projected — up to age 100 — and flags that this is after your plan date.

Bug Reports and Suggested Improvements

Please email all suggestions for improvements and any bug reports to: firecalc@personalfinances.me, thank you.

FIRE Number & Coast FIRE Calculator – FI Target & Coast Age

🎯 Your Plan

🔥 Results

📅 Year-by-Year Breakdown