RunLocalTools

FIRE calculator

Find out when you could retire early, how much you need, and how likely the plan is to last — with Coast and Barista FIRE, a Monte Carlo safety test, a historical backtest and a goal solver. Everything runs in your browser.

What it does

Tell this calculator how old you are, what you’ve invested, what you save and what you’d like to spend in retirement, and it works out your FIRE number — the portfolio you need before you can stop working — and the age you reach it. For example, if you’re 30 with 50,000 invested, save 25,000 a year and want to spend 40,000 a year, the starting numbers give a FIRE number of 1,000,000 and financial independence at 53, 23 years from now.

That’s only the first answer. The calculator also shows your Coast FIRE and Barista FIRE numbers, compares lean, regular and fat retirements, tests how likely the money is to last with thousands of simulated markets, replays your plan against your own historical returns, and solves backwards: how much you’d need to save, how much you’d need invested today, or how much you could spend to retire at the age you choose.

How it works

The FIRE number

Your FIRE number is your yearly spending divided by your withdrawal rate. At the classic 4%, 40,000 a year needs 1,000,000. If you expect a pension or other income, only the part of your spending that income doesn’t cover has to come from the portfolio — and because that income might not start until later, the number can change with your age. If part of your withdrawals will be taxed, the calculator grosses the withdrawal up so you still end up with the spending you asked for.

Real returns, so inflation is handled for you

Everything is worked out in today’s money. Enter a nominal return, your fund fees and inflation, and the calculator turns them into one real return — the starting figures (7% return, 0.2% fees, 2.5% inflation) come to about 4.2% a year. Prefer to enter a real return directly? Switch the mode and type it in. A switch in the panel shows any result in future, inflated money instead.

Saving first, then spending it down

Year by year, your savings are added at the end of each year and grow with your return; they can rise each year by an amount above inflation if you expect raises. One-off events — an inheritance, a house sale, a big purchase — land at the start of the age you give them. Once you retire, withdrawals come out at the start of each year, which is the cautious way round, and any pension or part-time income reduces what the portfolio has to pay.

Three ways of spending in retirement

  • Fixed real spending — the 4%-rule approach: the same spending every year, adjusted for inflation.
  • A fixed percentage — take the same share of whatever the portfolio is worth each year. It never runs out, but your spending rises and falls with the markets.
  • Guardrails (Guyton-Klinger style) — start from your planned spending, trim it by a set percentage if withdrawals become too large a share of the portfolio, and give yourself a raise when the portfolio does well. You choose the thresholds.

The Monte Carlo safety test

A single straight-line return hides the biggest risk in early retirement: a bad market right at the start. The safety test runs your retirement thousands of times, each with a different randomly generated sequence of yearly returns centred on your real return and with the volatility you choose. It reports the share of runs in which your money lasts to your end age, the typical and the unlucky outcomes, and when the failing runs ran out. The random numbers are seeded, so the same inputs and seed always give the same answer.

Backtest on your own data

Upload a CSV of yearly returns for whatever you invest in. Every possible stretch of your data, as long as your retirement, is replayed against your plan, and you see the share of starting years that would have worked, the worst and best, and which ones failed.

How to use it

  1. Enter your numbers in the panels at the top: your age, the age you’d like to retire, how long to plan for, what you have invested, what you save, your return and your spending. Fields that need attention are marked.
  2. Read the Overview: your FI age and year, FIRE number, progress, Coast FIRE and Barista FIRE, the lean/regular/fat table and the chart. If you’d rather retire at a fixed age than at the first possible moment, choose “At my target age” under Retirement spending.
  3. Open the Safety test to see the chance your money lasts and, if you have a file of returns, add it to backtest the plan.
  4. Open What if to see how your FI age moves as you save more, earn a different return, withdraw at a different rate or spend more or less — and to solve for the savings, starting portfolio or spending that gets you to your target age.
  5. Open Year by year for the full table, and download it as a CSV.
  6. Save scenarios — “part-time at 45”, “bigger house” — and compare up to three side by side with your current inputs.

Not sure what you really spend? Track a few months in the Digital Envelope Budgeter first. If you’re working out how much you can save from a paycheck, the Salary / Paycheck Calculator turns pay into take-home. And if high-interest debt is still in the picture, the Snowball vs Avalanche Debt Planner shows the cheapest order to clear it before investing.

Frequently asked questions

How is my FIRE number calculated?

Divide your yearly retirement spending by your withdrawal rate. Spending of 40,000 at a 4% rate gives 1,000,000; at 3.5% it gives about 1,143,000. If you’ll have income that covers part of your spending — a pension, rental income — only the remainder is divided. The calculator updates this for your age as that income starts, and shows what each rate does to your FI age in the What if tab.

What withdrawal rate should I use?

4% is the classic starting point, often traced to studies of 30-year retirements. A retirement that could last 40 or 50 years may call for something lower, and a flexible plan that cuts spending in bad years can start higher. Rather than trust one number, run the Safety test and the withdrawal-rate grid in What if, and see how much the answer moves.

What are Coast FIRE and Barista FIRE?

Coast FIRE is the amount that, left alone with no further saving, would grow to your FIRE number by your target retirement age. The calculator shows that amount, whether you’ve already reached it, and the age you’d reach it on your current plan. Barista FIRE is stopping full-time work earlier and covering part of your spending with part-time income: enter the yearly income and the age it lasts until, and you get the earliest age at which your money would last to your end age.

Why does the Monte Carlo chance differ from the headline FI age?

The FI age comes from the withdrawal-rate rule and a steady return. The Monte Carlo test asks a harder question — how often does the money survive when returns vary from year to year, including a bad start? Retiring the moment you reach your FIRE number can leave a real chance of running short over a long retirement, which is why the chance of success is shown beside the age. You can improve it by saving a little longer, spending a little less, using the guardrails strategy, or lowering the withdrawal rate.

Should I enter a nominal or a real return?

Either. If you enter a nominal return, also enter your inflation and fund fees and the calculator derives the real return — the figure that matters, since everything is in today’s money. If you already think in real returns, switch to “Real (after-inflation) return” and type it directly.

What file does the historical backtest need?

A CSV of yearly investment returns: either one column of returns, or a year column and a return column. Values can be percentages (7.5) or decimals (0.075) and are auto-detected, or you can set it. Tell the calculator whether the returns are already real or nominal; nominal ones are converted with your inflation figure. You need at least as many years of data as your retirement lasts.

Privacy

Everything runs on your device. The calculator makes no network requests of its own and loads no outside code — your figures, scenarios and returns file are never uploaded anywhere.

To save you retyping, it keeps your inputs and any scenarios in your browser’s local storage, and keeps a returns file you’ve added in the browser’s own file storage so it is still there after a refresh. All of it stays on your device. Clear saved data & reset removes your inputs and the returns file; delete saved scenarios from the Scenarios tab. Exported scenarios are ordinary files you save yourself, and pasting one in is handled entirely in your browser.

Limitations

  • This is a planning tool, not financial, tax or investment advice. It shows what your assumptions imply; real returns, inflation, taxes and your own life will differ.
  • Steps are annual. Taxes are a single average rate on withdrawals, other income is treated as already after-tax, and there is no modelling of account types, pension rules or healthcare costs — add costs you expect as one-offs or in your spending.
  • In the Monte Carlo test, returns are random only after you retire; the saving years use your steady real return. Randomness follows a bell-curve-shaped (lognormal) pattern and can’t capture every way markets behave.
  • The backtest uses only the data you supply and is limited by its length; past returns are no guarantee of future ones. The calculator doesn’t ship its own market history.
  • Coast FIRE counts any one-offs you’ve entered, but ignores changes to other income after the target age.