FIRE Calculator
Years to Financial Independence using the 4% safe withdrawal rule
Last updated: November 2025 · Based on Bengen (1994) and the Trinity Study (1998)
Your Numbers
What you need to live on each year after retiring
After inflation; 5% is a common assumption for a stock-heavy portfolio
4% = 25x expenses (Trinity). Use 3.25-3.5% for very early retirement.
FIRE Variants
Portfolio Trajectory to FIRE
Understanding FIRE Math
Why 25x Expenses?
The "25x expenses" rule comes from the inverse of the 4% safe withdrawal rate. If you can safely withdraw 4% of your portfolio each year, then your portfolio must be 1 / 0.04 = 25 times your annual spending. The original 4% number came from William Bengen's 1994 paper, in which he back-tested historical US stock and bond returns from 1926 onward and found that a 50/50 to 75/25 portfolio could sustain a 4% inflation-adjusted withdrawal for at least 30 years through every starting year, even retirees who began in 1929 or 1966.
Bengen's Updated SAFEMAX of 4.7%
In subsequent research published through 2020-2023, Bengen revised his SAFEMAX upward to about 4.7% when including small-cap and international stocks in the portfolio. The original 4% was conservative because it used only US large-caps and intermediate Treasuries. That said, other researchers (notably Wade Pfau) argue 3.0 to 3.5% is more appropriate when forward-looking return assumptions are lowered, when fees are included, or when the retirement period extends past 30 years. For FIRE retirees with potential horizons of 50+ years, a 3.25 to 3.5% rate is widely recommended.
Savings Rate Drives Time to FIRE
The single biggest lever in FIRE math is your savings rate as a percentage of take-home income. Pete Adeney (Mr. Money Mustache) famously showed that at a 50% savings rate (post-tax), you can reach FI in about 17 years from zero. At 65% savings rate, roughly 10.5 years. At 25%, around 32 years. Income matters, but the percentage you save matters more because it simultaneously reduces the expenses you need to cover and grows the pot.
Real Returns vs Nominal Returns
FIRE projections should use real (inflation-adjusted) returns, not nominal returns. The S&P 500 has averaged roughly 10% nominal annually long-term, but only about 7% after subtracting average inflation. Using nominal returns inflates the projection but makes the FIRE target wrong because you also need to inflate expenses. Using real returns and today's dollars sidesteps this. A 5% real return is a common moderate assumption for a stock-heavy portfolio.
Frequently Asked Questions
Where does the 4% rule come from?
The 4% rule was popularized by William Bengen in 1994 and confirmed by the 1998 Trinity Study (Cooley, Hubbard, Walz at Trinity University). Both studies back-tested historical US stock and bond returns from 1926 onward and found that withdrawing 4% of an initial portfolio (then adjusting that dollar amount for inflation each year) had a very high success rate of lasting 30 years for a 50/50 to 75/25 stock/bond portfolio. This is the origin of the 25x FIRE number.
Is 4% still safe? What is SAFEMAX?
Bengen has revised his work and now suggests SAFEMAX is closer to 4.7% with a more diversified portfolio that includes small-cap and international stocks. Others like Wade Pfau argue 3.0 to 3.5% is more appropriate, especially for retirements of 50+ years. For very early FIRE, 3.25 to 3.5% is the widely-cited prudent range.
What is sequence-of-returns risk?
Sequence-of-returns risk is the danger that a market crash in the first 5-10 years of retirement does outsized damage. Withdrawing while the portfolio is down locks in losses and leaves fewer shares to recover. Hold 2-3 years of expenses in cash or short bonds, consider a bond tent or rising equity glide path, and be willing to flex spending down in bad years.
How do you handle healthcare before Medicare?
Medicare starts at 65, so a 45-year-old FIRE retiree needs 20 years of coverage. Options: ACA marketplace plans (subsidies are MAGI-based, careful Roth conversions and capital gains harvesting can land you at $0 premium), a working spouse's plan, COBRA for 18 months, or healthshares (weaker protection). OBBBA preserved ACA subsidies for 2026 with some changes to the income cliff.
Lean vs Coast vs Barista vs Fat FIRE?
Lean: low budget, ~$1M target. Fat: generous budget, $2.5M+ target. Coast: accumulate enough early that the portfolio compounds to FIRE by 65 without further saving, then "coast" by covering only current expenses. Barista: work a low-stress part-time job (often for health insurance) that covers current spending while the portfolio grows untouched.
What is geographic arbitrage?
Earn a high-cost-area salary and retire in a lower cost-of-living area (Portugal, Mexico, Thailand, or low-cost US states like TN, TX, or rural New England). Annual expenses can drop 30-60%, shrinking the required FIRE number proportionally. Watch for visa rules, healthcare access, tax treaties (US taxes worldwide income for citizens), and distance from family.
When might the 4% rule fail?
When returns run materially below historical, when high inflation persists, when the retirement period exceeds 30 years (longer horizons need lower rates), or when spending is inflexible. The rule has near-100% historical success for 30 years but drops for 50+ year horizons. Use 3.25 to 3.5% for very early FIRE and stay willing to flex spending in down years.