What does a historical FIRE backtest do?

A historical FIRE backtest replays the same withdrawal plan across many rolling historical return windows so you can see how different retirement start years would have affected the outcome.

How is this different from Monte Carlo?

Historical backtesting reuses past return windows, while Monte Carlo creates many random future paths from your assumptions. The two tools answer related but different planning questions.

Why do retirement start years matter?

Because retiring into a weak sequence can hurt a withdrawal plan much more than retiring into a strong sequence, even when the spending rule stays the same.

Historical FIRE Backtest Calculator

Test one withdrawal plan across many retirement start years. This version uses a built-in annual real return proxy series from 1926 to 2024, so spending stays constant in real terms and inflation is already baked into the return path.

Pick a starting balance, spending level, and retirement length to see how the same plan would have behaved across rolling start years in the built-in real return series.

Success rate –

Best start year –

Worst start year –

Median ending value –

How To Read This

This page answers a different question than Monte Carlo. Instead of generating random paths, it replays many rolling windows from the same built-in real return series from 1926 to 2024. That makes it useful for asking “how would this plan have behaved if I had retired into a rough patch versus a friendly one?”

Backtest Windows

Start year	End year	Outcome	Failure year	Ending value

Historical Backtest FAQ

What does this historical FIRE backtest show?

It shows how the same withdrawal plan would have behaved if retirement had started in many different historical-style windows. That helps surface strong and weak starting points for the exact same plan.

Is this the same as a Monte Carlo simulation?

No. This page replays rolling historical real return windows, while the Monte Carlo FIRE Simulator generates many random future paths from your assumptions.

What should I compare this with?

If you want to isolate early bad years versus late bad years, use the Sequence Risk Calculator. If you want a rough spending-based target first, start with the 4% Rule Calculator.