What a FIRE number actually is
Your FIRE number is the amount you need invested so that a fixed percentage withdrawal each year — your safe withdrawal rate — covers your annual expenses indefinitely. The standard shortcut is the 4% rule, drawn from the 1998 Trinity Study: withdraw 4% of a diversified portfolio in year one and adjust for inflation after that, and historically the money outlasted 30-year retirements in the large majority of market scenarios. Flip the math around and a 4% withdrawal rate implies a FIRE number of 25× your annual expenses — exactly what the calculator above computes from whatever rate you enter.
Why the withdrawal rate is the whole argument
Change the withdrawal rate and the number moves a lot. At 4%, $48,000/year needs $1.2M. Drop to 3.5% — a common choice for early retirees planning a 40+ year horizon rather than the Trinity Study's 30 — and the same expenses need about $1.37M. Push to 5% and it's $960,000. None of these rates are guaranteed; they're historical backtests. The lower you go, the more cushion against a bad sequence of early returns, at the cost of needing more money and more years to get there.
FIRE isn't one number
- Lean FIRE — retiring on a tight, minimal-expense budget, often under $40k/year; a smaller number, reached faster.
- Fat FIRE — retiring at a comfortable-or-better lifestyle, often $100k+/year; a much larger number.
- Coast FIRE — you've invested enough that growth alone, with no further contributions, reaches a full FIRE number by a normal retirement age — so you can downshift to lower-stress work today.
- Barista FIRE — a hybrid: enough invested to mostly retire, plus light part-time income to cover a remaining expense or health-insurance gap.
All four use the same 25×-style math above; they differ in the expense number you plug in and whether contributions continue.
The two levers that actually move your date
Run your own numbers above, then try moving the two contribution-side inputs by a realistic amount. Doubling the monthly contribution consistently cuts more years off the date than a couple of extra points of assumed return, because contributions are current, guaranteed dollars, while a higher return assumption is a bet you don't control. The lever the calculator doesn't touch directly, but which drives everything, is your expense line: cutting annual expenses by $5,000 does two things at once — it shrinks the FIRE number itself (25× less) and frees up more to invest. That's why FIRE planning obsesses over the expense side at least as much as the return side.
This calculator gives you the target and the pace; it can't hold 20–30 years of contributions, market swings, and expense changes in view at once. For that, our Net Worth Tracker keeps a running monthly record of your invested assets against the target line, so you can see whether reality is tracking your projection or drifting off it.
Frequently asked questions
- What withdrawal rate should I use — 3%, 3.5%, or 4%?
- 4% comes from the Trinity Study's 30-year horizon; many people planning to retire in their 30s or 40s use 3.5% or even 3% for a longer runway and more safety margin against a bad early sequence of returns. Try the calculator at a couple of rates and see how much the number moves before committing to one.
- Does this calculator account for Social Security or a pension?
- No — it assumes your investments alone cover 100% of expenses. If you expect Social Security, a pension, or rental income later, you can reasonably lower the annual expenses figure by that future amount, since your portfolio then only needs to cover the gap.
- What's the difference between FIRE and Coast FIRE?
- Full FIRE means your portfolio alone covers your expenses today. Coast FIRE means you've invested enough that, left alone with no further contributions, growth gets you to your full FIRE number by a normal retirement age — so you could stop contributing, or take lower-paying and lower-stress work, well before hitting the number outright.
- Does this calculator account for inflation?
- It computes nominal dollars using whatever return rate you enter. If you use an inflation-adjusted (real) return — often modeled around 5–7% for stocks after inflation — the FIRE number and projected date come out in today's purchasing power terms, which is usually the more useful way to plan.