Free calculator · no account
FIRE number calculator
Your FIRE number is the portfolio that supports your retirement spending indefinitely. It takes two inputs — what you’ll spend, and the withdrawal rate you trust.
That’s $5,000/month of spending. The classic 4% rule is the 4% setting; drag lower for a more conservative target.
How the math works
FIRE number = annual spending / withdrawal rate
At the classic 4% rule that’s spending × 25 — $60,000 a year needs $1.5 million. A more conservative 3.5% rate is spending × ~28.6; a 5% rate is spending × 20. The rate embodies how confident you are the portfolio survives a long retirement — it’s the single most consequential assumption in FIRE planning, which is why the slider is front and center.
Where does 4% come from? Our FIRE number guide walks the full logic, and the 4% rule article covers the research behind the rate itself.
What this calculator skips
Spending ÷ rate is the honest core, but it treats your spending as one flat number and your portfolio as one untaxed pot. In practice, Social Security and pensions reduce what the portfolio must cover, taxes depend on which accounts you draw from, and spending itself shifts across retirement. Each of those moves the real target.
The full Calcifir planner models all of it — free to start. Build your real plan.
Common questions
Should I use gross or after-tax spending?
Use what you actually spend in a year, in today’s dollars — then remember the answer is slightly optimistic, because withdrawals from pre-tax accounts get taxed on the way out. The full planner handles that gross-up for you.
Does Social Security lower my FIRE number?
Effectively yes — once benefits start, the portfolio only has to cover the gap. A simple spending ÷ rate number ignores that, so treat it as an upper bound if you expect meaningful benefits.
Is 25× spending always right?
25× is just the 4% rule restated. Longer retirements (early retirees), heavier bond allocations, or wanting money left over all argue for a lower rate — that’s exactly what the slider is for.
More free tools: Coast FIRE calculator · 4% rule calculator · quick retirement check