How this is calculated
- Your FI number — your withdrawal rate. The Trinity-study heuristic says a
diversified portfolio historically survived a 30-year retirement when the first-year
withdrawal was 4% (inflation-adjusted thereafter). Inverting it gives your target:
FI number = annual spending ÷ safe withdrawal rate. At the default 4% that's25 × spending— spend $50,000/yr and your target is $1,250,000. The withdrawal rate is adjustable here: a more conservative 3.5% multiplies spending by ~28.6× ($1,428,571), and 3% by ~33.3× ($1,666,667). Why lower it? The 4% rule is built on US historical data and a ~30-year horizon; early retirees with 40–50-year horizons, or unlucky early-years market crashes (sequence-of-returns risk), often plan around 3–3.5%. Treat 25× as the optimistic baseline and dial the rate down for more margin. - Compound growth, month by month. Each month the portfolio grows by
one-twelfth of the annual return, then your contribution lands:
balance ← balance × (1 + r/12) + contribution. Over n months that equals the closed formFV = P·(1+r/12)ⁿ + c·((1+r/12)ⁿ − 1)/(r/12)where P is your starting balance and c the monthly contribution. - Inflation adjustment. With "today's dollars" on, the projection uses
the real return
r_real = (1 + r)/(1 + i) − 1(7% nominal at 2.5% inflation ≈ 4.39% real), so the curve, the FI number, and every milestone stay in today's purchasing power — an apples-to-apples comparison, since the FI number is 25× today's spending. With it off, the curve is nominal and will look faster than it really is against a today's-dollars target. - The FIRE date. The first month the projected balance reaches the FI number, counted from July 2026, becomes your crossover — shown as years + months, a calendar month, and (if you gave your age) the age you'd be.
- Coast-FIRE. This is the amount that, invested today and left
untouched with zero further contributions, would compound on its own to
your FI number by your target retirement age:
Coast number = FI ÷ (1 + real return)^(years to retirement). We always use the real return here, because the FI number is in today's dollars. If your current invested savings already meet or beat that number, you've hit Coast-FIRE — you could stop saving and still retire on time (you'd still need income to cover spending until then). If not, we show how much more you'd need invested now to coast.
What this doesn't model: taxes and account types (401k/Roth/taxable), variable returns and market crashes, changing contributions or spending, Social Security or pensions, fees. It is a smooth-curve planning estimate — reality will be lumpier.
Learn more
The 4% Rule Explained How much you actually need invested to retire — the 25× math behind your FI number.Frequently asked questions
What is the 4% rule (and the 25× rule)?
The 4% rule, from the Trinity study, found that withdrawing 4% of a diversified portfolio in year one of retirement (then adjusting for inflation) survived most historical 30-year periods. Inverted, it means you need roughly 25 times your annual spending invested — that 25× figure is your FI number, and it is what this calculator targets. It is a planning heuristic, not a guarantee: sequence-of-returns risk, longer retirements, and fees can all require a lower withdrawal rate.
Is a 7% annual return realistic?
7% nominal is close to the long-run average of a diversified US stock portfolio before inflation; after roughly 2.5–3% inflation it corresponds to about 4–4.5% real. Real-world results vary enormously decade to decade — the default is a directional planning assumption as of July 2026, not a prediction. Test lower numbers (5%) to see how sensitive your date is.
Does this calculator include taxes?
No. It projects pre-tax portfolio growth. Taxes depend on your account mix (401k, Roth IRA, taxable brokerage), your withdrawal strategy, and future tax law. A common approximation is to include expected taxes in your annual spending number, which raises your FI number accordingly.
What is Coast-FIRE?
Coast-FIRE is the point where your existing portfolio, with zero further
contributions, would compound on its own to your FI number by your target
retirement age. Once you've hit it you can stop investing for retirement (you'd still work
to cover day-to-day spending, but not to save) and still retire on time. This calculator
computes it directly: enter your current age and target retirement age and read the
Coast-FIRE number in the results — it's your FI number discounted back to today
at the real return, FI ÷ (1 + real return)^(years to retirement). If your
invested savings already meet that number, the status line confirms you're coasting;
otherwise it shows how much more you'd need invested now.
Why would I use a withdrawal rate other than 4%?
The 4% rule assumes a ~30-year retirement on US historical data. If you're retiring early with a 40–50-year horizon, worried about a bad sequence of early-retirement returns, or you just want more margin, a lower rate is safer — but it raises your FI number. Dropping the withdrawal rate from 4% to 3.5% moves your target from 25× to about 28.6× your annual spending; 3% makes it 33.3×. A higher rate (say 4.5–5%) lowers the target but leans on strong markets and a shorter horizon. Adjust the Safe withdrawal rate field to see your FI number, FIRE date, and Coast-FIRE number all update.
Is my financial data stored or sent anywhere?
No. Everything runs in your browser; nothing you type is sent to a server. The "copy share link" button encodes your inputs into the link itself, so only people you share that link with can see them.
This calculator is an educational estimate, not financial advice, not investment advice, and not a recommendation to buy any security. Markets do not return a smooth 7% — verify your plan with a fiduciary advisor. No liability is accepted for decisions made from these results.