Coast FIRE Calculator

1. Enter your current age so the tool knows how many years your money can compound.
2. Set your target retirement age — the year you want invested assets to cover your spending.
3. Input expected annual expenses in retirement (today's dollars). Many planners start near 70–80% of current spending.
4. Enter your current retirement savings across 401(k), IRA, brokerage, and similar accounts.
5. Adjust the real return rate (default 7%) to reflect your expected return after inflation.

First the calculator estimates your traditional FIRE number using the 4% rule: annual retirement expenses divided by 0.04. That is the portfolio size that could theoretically support those expenses with a 4% initial withdrawal rate. Coast FIRE asks a different question: how much do you need invested today so that amount, left alone, grows to the FIRE number by retirement? The tool discounts the FIRE number backward by your assumed real return over the years between now and retirement.

FIRE number = Annual expenses ÷ 0.04
Coast FIRE number = FIRE number ÷ (1 + real return)^years_to_retirement
Gap = max(0, Coast FIRE number − current savings)

Suppose you are 30, plan to retire at 65, expect $60,000 of annual retirement spending, already have $50,000 invested, and assume a 7% real return. Your FIRE number is $60,000 ÷ 0.04 = $1,500,000. You have 35 years for compounding, so the Coast FIRE number is $1,500,000 ÷ (1.07)^35 ≈ $142,000. With $50,000 saved, you still need roughly $92,000 more to "coast." Once you reach that ~$142,000 invested, you could stop retirement contributions (in this model) and let growth carry the portfolio to $1.5M by age 65 — while still covering living costs from income. Change the return rate or retirement age and the coast number moves sharply: fewer years or a lower return means you need more capital today.

FIRE number

The estimated portfolio you would need at retirement to support your stated annual expenses under a 4% withdrawal assumption. It is a planning benchmark, not a guarantee of sustainable spending.

Coast FIRE number

How much you need invested today so that, if left untouched and growing at your assumed real return, it reaches the FIRE number by your retirement age.

You have / Still need

Your current savings versus the remaining gap to the Coast FIRE number. A zero gap means you have hit coast status under these assumptions.

Progress

Current savings as a percentage of the Coast FIRE number — a quick view of how close you are to the coasting threshold.

• Treating the 4% rule as a personal promise — sequence of returns, longevity, and spending changes can require a different withdrawal rate.
• Using a nominal stock-market return (e.g. 10%) instead of a real return after inflation, which understates how much you need today.
• Ignoring taxes, fees, and account-type rules when counting "current savings."
• Assuming you can truly contribute $0 after Coast FIRE while still paying for healthcare, housing inflation, or college costs from wages alone.
• Planning Coast FIRE without an emergency fund and short-term cash buffer outside the long-term portfolio.

The calculator assumes a constant real return compounded annually, no additional contributions after the Coast FIRE number is reached, expenses expressed in today's dollars, and a FIRE number equal to annual expenses ÷ 0.04 (the classic 4% rule framing). It does not model taxes, sequence-of-returns risk, variable spending, Social Security, pensions, or investment fees. Results are educational estimates for planning conversations, not a personalized forecast.

• SEC Investor.gov — Compound interest
• FINRA — Saving for retirement
• AlgoFinanceLab — FIRE & early retirement guides

Dig deeper with our FIRE movement and early retirement guide, or try Passive Income Tracker and Asset Allocation Planner.

Estimates only — not financial, lending, or investment advice. Decisions should be based on your full situation and professional guidance where appropriate.