Years to FIRE
14.3
FI number: $1.25M
Savings rate44%
Coast FIRE today$310K
Lean FIRE (3%)$1.67M
Fat FIRE (2.5%)$2M
25x your annual spending. The Trinity Study endpoint, the Mustache plan, the math the FIRE community lives by.
The 4% rule and its corollary — 25× expenses — comes from William Bengen's 1994 paper "Determining Withdrawal Rates Using Historical Data" and the Trinity Study (Cooley/Hubbard/Walz, 1998). Both tested fixed-percentage withdrawals (adjusted for inflation each year) against rolling 30-year periods of US stock and bond returns since 1926. 4% succeeded in every 30-year window tested. The math: 1 ÷ 0.04 = 25, so a portfolio of 25× annual expenses sustains a 4% inflation-adjusted withdrawal indefinitely.
FI — target portfolio · P — current portfolio · S — annual savings · r — annual returnFor early-retirement horizons of 40-50 years, most current research (Pfau, ERN, Morningstar 2024) lands at 3.25-3.5% as the more defensible starting rate, which translates to 28-31× expenses.
From Mr. Money Mustache's 2012 "Shockingly Simple Math" essay, refined repeatedly. Assumptions: 5% real return, 4% withdrawal rate, starting from zero. The relationship is mechanical — high savings rates compress timelines dramatically.
| Savings rate | Years to FI from $0 | Lifestyle |
|---|---|---|
| 10% | 51 years | Traditional retirement at ~65 |
| 15% | 43 years | Fidelity-recommended baseline |
| 25% | 32 years | FIRE-curious |
| 40% | 22 years | Standard FIRE |
| 50% | 17 years | Aggressive FIRE |
| 65% | 10.5 years | Lean FIRE / extreme frontloading |
| 75% | 7 years | Tech-comp lean FIRE / dual-income high earners |
If you save half your take-home, you accumulate one year of expenses for every year you work. At FI when you have 25 years stockpiled, that's exactly 25 years of 50% savings = 25 years of full work. The income on either side of the equation drops out — what matters is the ratio of saving to spending.
| Variant | FI multiple | Annual spending | Lifestyle |
|---|---|---|---|
| Lean FIRE | 25-30× | $25-40k | Minimalist, often geo-arbitrage |
| Standard FIRE | 25× | $50-80k | Middle-class lifestyle |
| Fat FIRE | 30-40× | $150k+ | Upper-middle / comfortable luxury |
| Coast FIRE | ~5-10× | Cover current | Compounding does rest by 65 |
| Barista FIRE | 15-20× | ~half from portfolio | Part-time work for healthcare |
| Slow FI | 25× | Variable | Optimize lifestyle along the way |
The single biggest practical obstacle to early retirement in the US. Pre-65 ACA marketplace premiums for a 60-year-old can run $1,000-$2,000/month before subsidies. Plan $20-30k/year of pre-65 healthcare unless your spouse has employer coverage or you're VA-eligible.
The temptation to upgrade housing, cars, and travel as income peaks is what derails most FIRE plans. Each $1 of annual spending added increases the FI Number by $25 (at 4% SWR) — a $200/month subscription habit becomes $60,000 in required portfolio.
The 4% rule was derived for 30-year retirements. Using it for 50-year horizons inflates the apparent success rate. Drop to 3.25-3.5% for true early retirement to maintain the same historical safety margin — or accept that you may need part-time income in down years.
Sources: Bengen 1994 Journal of Financial Planning; Cooley/Hubbard/Walz 1998 Trinity Study; Mr. Money Mustache "The Shockingly Simple Math" (2012); Wade Pfau "Safety-First Retirement Planning"; Karsten Jeske "Safe Withdrawal Rate Series" (Early Retirement Now); Morningstar "The State of Retirement Income" (2024 update).
For 30-year retirements, yes — Bengen (1994) and Trinity Study (1998) found 4% succeeded across every rolling 30-year period since 1926, and Morningstar's 2024 update confirmed the same conclusion. For 40-50 year horizons, most researchers including Wade Pfau, Big ERN, and Karsten Jeske argue 3.25-3.5% is more defensible, primarily because of sequence-of-returns risk over longer windows.
You've saved enough that compound growth alone will reach your full FI number by traditional retirement age, even without further contributions. Practical use case: hit Coast FIRE in your 30s and you can downshift to a lower-paying but more enjoyable career — your retirement is already on track. The Coast number is FI-number ÷ (1+r)^years-to-traditional-retirement. At 7% real with 25 years to retirement, Coast is roughly 18% of your full FI number.
Mr. Money Mustache's 2012 "Shockingly Simple Math" essay popularized: years to FI depend almost entirely on savings rate, not income. At a 5% real return, a 10% savings rate takes ~50 years; 25% takes ~32 years; 50% takes ~17 years; 75% takes ~7 years. The math: if you save half your take-home, you accumulate one year of expenses for every year you work — at FI when you have 25 years stockpiled, that's 25 years of 50% savings.
Variants based on lifestyle and timing. Lean FIRE: minimalist living, often $25-40k/year. Standard FIRE: middle-class, ~25× expenses. Fat FIRE: comfortable upper-middle, often 30-40× expenses with 2.5-3% withdrawal. Coast FIRE: compounding alone gets you to traditional retirement; you only cover current expenses. Barista FIRE: investment income for most expenses, supplemented by part-time work (often for healthcare). Most early retirees mix these over a career.
It's the dominant risk for early retirees. A bad first 5-10 years of returns can permanently impair the portfolio even if average returns over the full retirement match historical norms. Mitigations: (1) cash buffer of 1-3 years of expenses; (2) bond tent — higher fixed-income allocation entering retirement, gliding back to equities; (3) dynamic withdrawal (Guyton-Klinger guardrails) — cut in down years, raise in up years; (4) part-time income in early years.
Three options. (1) Taxable brokerage — savings outside retirement accounts, drawn at any age with only capital-gains tax. (2) Roth IRA contributions can come out any time tax-free and penalty-free. (3) Roth conversion ladder — convert Traditional to Roth in low-income years, wait 5 years, then access penalty-free. SEPP/72(t) substantially-equal-periodic-payments works too. Most early retirees use a mix.
The single biggest practical obstacle to early retirement in the US. Medicare starts at 65; until then you need ACA marketplace coverage. Premiums for a 60-year-old can run $1,000-$2,000/month before subsidies. The ACA premium tax credit phases out as income rises — many early retirees deliberately keep MAGI low (in part by living off Roth contributions) to qualify for full subsidies. Plan $20-30k/year of pre-65 healthcare.
Most research converges on 3.25-3.5% for 40-50 year horizons. Wade Pfau's Monte Carlo work using current valuation-aware assumptions suggests starting in the low 3% range to maintain a 90%+ success rate over 50 years. Karsten "Big ERN" Jeske's exhaustive Safe Withdrawal Series lands in similar territory. The 3.5% rule restated: FI Number ≈ 28-29× annual expenses, vs the 4% rule's 25×.
Conservatively, yes — but discount it. The 2026 average benefit is roughly $2,000/month at FRA (67). The Trustees project the trust fund will be depleted around 2034 if Congress doesn't act, with a 17% benefit reduction following — most FIRE planners model 70-80% of projected benefits as a planning haircut. SS provides meaningful income from FRA onward, lowering portfolio drawdown rate during years 65+.
FIRE plans often optimize around the 0% LTCG bracket. Long-term capital gains are taxed at 0% up to $48,350 single / $96,700 MFJ of taxable income in 2026 per IRS Rev. Proc. 2025-32. An early retiree living off $60-80k of mostly long-term gains and Roth contributions can realize federal tax bills near zero. Pair with strategic Roth conversions during low-income years to permanently shift Traditional balances to Roth at low rates.