Your FIRE Number
Years to FIRE
Projected FIRE Date
Results assume constant annual returns and contributions. Actual investment returns will vary. This calculator is for guidance only.
Table of Contents
Why this calculator matters
FIRE planning is a two-variable optimization — a target portfolio size (your FIRE number) and a time-to-reach-it (your savings rate). This calculator computes both, lets you stress-test the assumptions behind the 4% rule, and shows how small changes to expenses or contributions move the finish line by years.
How the FIRE number and timeline are calculated
The FIRE number itself is simple division — expected annual expenses divided by your chosen safe withdrawal rate:
FIRE number = Annual expenses ÷ Withdrawal rate
The years to reach it is the future-value-of-annuity equation solved for time:
FV = B0(1 + r)t + C × [ ((1 + r)t − 1) ÷ r ]
- FV — target portfolio (your FIRE number)
- B0 — current savings & investments
- C — annual savings/contributions
- r — expected annual return (decimal)
- t — years required (the unknown)
Because t appears in the exponent, the calculator solves iteratively year by year until the running balance reaches the FIRE number.
Worked example using the calculator's defaults ($50,000 expenses, $50,000 current savings, $20,000/year contributions, 7% return, 4% withdrawal rate):
- FIRE number = 50,000 ÷ 0.04 = $1,250,000
- Year 1: 50,000 × 1.07 + 20,000 = $73,500
- Year 5: ~$185,000
- Year 10: ~$374,000
- Year 20: ~$1,015,000
- Year 22 (approx): crosses $1.25M → FIRE achieved in ~22 years
Now try lowering expenses to $40,000 (FIRE number drops to $1M) or raising contributions to $30,000/year — either move shaves 4–6 years off the timeline.
Savings rate vs years to FIRE
Assuming you start from zero, earn 5% real return, and live on what's left after saving. This is the table that defined the FIRE movement (Mr. Money Mustache, 2012):
| Savings rate | Years to FIRE | Notes |
|---|---|---|
| 5% | ~66 years | Default US median — doesn't really achieve FIRE |
| 10% | ~51 years | Traditional financial planning rate |
| 20% | ~37 years | Above-average saver |
| 30% | ~28 years | Lean toward FIRE territory |
| 40% | ~22 years | Aggressive saver |
| 50% | ~17 years | Classic FIRE territory |
| 65% | ~10.5 years | Lean FIRE / high-income FIRE |
| 75% | ~7 years | Extreme FIRE |
The math is non-linear because raising your savings rate does two things simultaneously: it grows the portfolio faster, AND it lowers the lifetime expenses you'll need to fund. This is why expense reduction beats income increase dollar-for-dollar on the FIRE timeline.
Withdrawal rate vs FIRE multiplier
The withdrawal rate you choose changes your target dramatically. For a $50,000/year retirement spend:
| Withdrawal rate | Multiplier (1/rate) | FIRE number | Typical use case |
|---|---|---|---|
| 5.0% | 20× | $1,000,000 | Optimistic / short horizons <25 years |
| 4.0% | 25× | $1,250,000 | Classic Trinity Study, 30-year horizon |
| 3.5% | ~28.6× | $1,430,000 | FIRE community standard for 40+ year retirement |
| 3.25% | ~30.8× | $1,540,000 | Conservative for early retirees <40 |
| 3.0% | ~33.3× | $1,670,000 | Perpetual portfolio / safety-first |
The original Trinity Study tested 30-year horizons. A 35-year-old retiree might need their portfolio to last 50–60 years — well beyond the data the 4% rule was validated against. The honest FIRE community standard has drifted from 4% toward 3.5% for younger retirees.
Lean, Fat, Coast, Barista — the FIRE variants
| Variant | Annual spend target | Portfolio needed (at 4%) | Defining feature |
|---|---|---|---|
| Lean FIRE | <$40k | <$1M | Aggressive frugality, geo-arbitrage |
| Regular FIRE | $40–100k | $1–2.5M | Median US household lifestyle |
| Fat FIRE | $100k+ | $2.5–5M+ | Comfortable/luxury lifestyle, travel |
| Coast FIRE | Anything | Enough today that compounding alone reaches full FIRE by ~60–65 | Active income still covers current expenses |
| Barista FIRE | Partial | Portfolio covers part, part-time work covers the rest | Often pursued for healthcare/social benefits |
Coast FIRE is the gentlest variant — you stop adding to the portfolio once it's large enough to compound to full retirement on its own. If you have $200k saved at age 30, that compounds to roughly $1.5M by 65 at 7% with no further contributions. From that point on, you only need to earn enough to cover today's expenses.
Limitations of this calculator
- Constant return assumed. Real markets are volatile. A simple constant-return model can be off by years in either direction depending on actual sequence of returns. For more rigorous planning, run Monte Carlo simulations (cFIREsim, FICalc, Engaging Data).
- Inflation handled implicitly. The 4% rule works in real (inflation-adjusted) terms. If you plug in a 7% nominal return and current-dollar expenses, you're implicitly assuming a real return of about 4–5% — reasonable, but be aware of the mixing.
- Healthcare gap ignored. US retirees under 65 face Medicare-eligibility gap. Private insurance can run $500–2,000/month per person, easily adding $6–24k to annual expenses. ACA subsidies help if your income drops, but the math is fragile.
- No Social Security credit. Most FIRE plans don't lean on SS, but eligible workers can claim from 62. A $1,500/month SS check from age 67 onwards covers $18k/year of expenses you don't need the portfolio to cover.
- Tax drag not modeled. Withdrawals from taxable accounts trigger capital gains tax; traditional IRA/401(k) withdrawals are taxed as income. Pure Roth is the most efficient. The 4% rule was based on pre-tax portfolios — the after-tax safe rate depends on your account mix.
- Lifestyle creep. Expenses tend to drift up over a career. The "current expenses" you model may not be your real long-term spend.
Sources & references
- Cooley, Hubbard & Walz (1998) — the original Trinity Study — foundation of the 4% rule.
- Michael Kitces — safe withdrawal rate research — updated analysis suggesting 3.5% for longer retirements.
- Mr. Money Mustache (2012) — "Shockingly Simple Math Behind Early Retirement" — original savings-rate vs years-to-FIRE table.
- Morningstar — State of Retirement Income — ongoing analysis of sustainable withdrawal rates under current market conditions.
- Healthcare.gov — ACA marketplace for pre-Medicare retirees.
FAQs
Your FIRE number is the portfolio size that lets investment returns cover your annual expenses indefinitely. The standard formula is annual expenses ÷ safe withdrawal rate, which equals 25 × expenses at the classic 4% rule. Spending $50,000/year? FIRE number is $1.25 million. Spending $80,000/year? You need $2 million. Lowering your expenses by $10,000 cuts your FIRE number by $250,000 at a 4% rate — which is why frugality is the highest-leverage FIRE strategy.
From the 1998 Trinity Study by Philip Cooley, Carl Hubbard and Daniel Walz. They tested historical US stock/bond data from 1926–1995 and found a 50–75% stock portfolio could sustain 4% inflation-adjusted withdrawals across virtually every rolling 30-year period without running out. Newer research (Pfau, Kitces, Bengen himself) suggests that 4% works for 30 years but may be aggressive for the 50+ year horizons typical FIRE retirees face — many now use 3.25–3.5%.
Far more than people expect. At a constant 5% real return: a 10% savings rate takes ~51 years to FIRE, 20% takes ~37 years, 40% takes ~22 years, 50% takes ~17 years, 65% takes ~10.5 years, and 75% takes ~7 years. This is Mr. Money Mustache's famous savings rate table — the math is brutally non-linear because saving more does two things at once: it grows the portfolio faster AND lowers the lifetime expenses you need to cover.
Lean FIRE: retire on a minimal budget (<$40k/year for a couple), requiring <$1M. Fat FIRE: retire on a comfortable-to-luxurious budget ($100k+/year), requiring $2.5–5M+. Coast FIRE (or Barista FIRE): save enough early that the existing balance compounds to full retirement by traditional age, while part-time or low-stress work covers current expenses — you're "coasting" on prior savings. Different lifestyle bets, same underlying math.
Sequence-of-returns risk. A 30%+ drop in the first few years of retirement, combined with ongoing withdrawals, can permanently damage a portfolio in ways later recoveries can't fully fix. A retiree who hit FIRE in 2000 just before the dot-com crash needed nearly a decade longer to be safe than one who retired in 2009. Mitigations: keep 1–3 years of expenses in cash/short-term bonds, use a variable withdrawal strategy (cut spending in down years), or maintain some flexible income.