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FIRE Calculator: Test Financial Independence Against Real Market History

Model your FIRE number — starting portfolio, planned spending, and years until traditional retirement age — and test it against real historical market data instead of a single average-return projection.

Stress-test your FI number

What the FI number represents

The FIRE (Financial Independence, Retire Early) number is commonly estimated as roughly 25 times annual expenses — the inverse of a 4% withdrawal rate. It's a starting point for a conversation, not a guarantee, and that's especially true for early retirement, where the horizon is longer than the 30-year window most classic withdrawal-rate research assumes.

Why early retirement changes the math

Someone retiring at 35 may need a portfolio to last 50 years or more, not 30 — meaningfully longer than most historical safe-withdrawal-rate research covers, and with more exposure to multiple full bear-market cycles along the way.

This calculator's test window caps at 30 years per run. A practical way to approximate a longer FIRE horizon: test a lower withdrawal amount as a rough safety margin, or treat one run's ending balance as a rough starting point for a second 30-year window to sanity-check what a 50+ year span might look like.

Coast FIRE, Lean FIRE, Fat FIRE — same tool, different inputs

The common FIRE variants — Lean (minimal spending), Fat (higher spending), Coast (stop contributing but let the portfolio grow untouched until traditional retirement age), Barista (part-time income covers some expenses) — don't need separate tools. Each just changes the starting corpus, the monthly withdrawal or contribution amount, or the allocation you test here, not the underlying method.

Modeling the savings phase, not just the withdrawal phase

Getting to a FIRE number is its own multi-year test, separate from living off it afterward. Switching the amount field to Contribute instead of Withdraw lets you model that accumulation phase directly — for example, a hypothetical $50,000 starting balance with a $2,000 monthly contribution, tested against real historical returns, shows how a savings plan would have actually grown (or stalled) depending on when it started.

Running the accumulation phase and the withdrawal phase as two separate tests — rather than expecting one run to do both — keeps each result easier to read and compare.

How to use this calculator for a FIRE plan

Enter your current savings as the starting portfolio, your planned monthly spending as the withdrawal, and an inflation adjustment. Build an allocation — the preset above uses a more equity-heavy split common among younger FIRE plans with a longer horizon and higher risk tolerance, but nothing here is a recommendation to match it.

Test a range of withdrawal amounts and watch where the historical survival rate starts dropping — that inflection point is often more informative than any single “pass/fail” result.

Limitations to keep in mind

This tool doesn't model part-time or side income (common in Coast and Barista FIRE plans), healthcare costs before Medicare eligibility (a real early-retirement-specific risk), or tax drag from account types and withdrawal order. Those are real, material factors for an early-retirement plan that a market-history stress test alone can't capture.

It also runs one glidepath-free scenario at a time — a real plan often shifts allocation gradually as retirement approaches, where this tool tests a fixed allocation for the whole period. Testing the same plan with a more conservative allocation is a reasonable way to approximate what a late-stage shift toward bonds might do to the results.

Frequently asked questions

What is a FIRE number?

It's the portfolio size — commonly estimated as roughly 25 times annual expenses — that a Financial Independence, Retire Early plan targets before stopping traditional work. It's a rough guideline, not a precise or guaranteed figure.

How many years of expenses do I need saved for FIRE?

A common rule of thumb is 25x annual expenses (a 4% withdrawal rate), but that figure was calibrated on a traditional 30-year retirement horizon. Early retirees with longer horizons often test lower withdrawal rates to build in more of a margin.

Does this calculator handle Coast FIRE or Barista FIRE?

Not as a dedicated mode, but you can approximate either: model the accumulation phase using the Contribute toggle, then separately test the withdrawal phase once contributions stop, using your current or projected balance as the starting portfolio.

Why does the test window cap at 30 years if FIRE means longer retirements?

Thirty years is the longest single rolling window most of the available historical fund data can reliably support test across many starting months. For longer FIRE horizons, testing a more conservative withdrawal rate is a practical way to build in extra margin.

Should I use a lower withdrawal rate for early retirement?

Many FIRE planners discuss lower rates (often cited in the 3-3.5% range) specifically because of the longer time horizon involved, though this isn't financial advice — testing several withdrawal rates against historical data yourself is exactly what this calculator is for.