The 25× rule explained — your FI number and how to actually hit it

The 25× rule is the simplest retirement-planning shortcut ever invented. Multiply your annual expenses by 25, and that's the portfolio size you need to retire. It works because of the 4% safe withdrawal rate (1/25 = 4%) — the empirically-tested rate at which a balanced portfolio can sustain inflation-adjusted withdrawals for 30 years.

The basic math

Annual expenses → multiply by 25 → that's your FI number. $30,000/year = $750K. $50,000/year = $1.25M. $80,000/year = $2M. $120,000/year = $3M. The number depends entirely on your spending, not your income.

Where the 4% comes from

In 1998, three Trinity University professors back-tested portfolio survival across every 30-year period in US market history. A 50/50 stock/bond portfolio withdrawing 4% (inflation-adjusted) survived 95%+ of historical periods. The "4% rule" was born — and 1/4% = 25, hence the 25× rule.

The early-retirement adjustment

The 4% rule was tested for 30-year retirements. If you retire at 45 and need 40-50 years of withdrawals, 4% becomes risky. Most early-retirement researchers (Big ERN, Karsten Jeske) recommend 3.25-3.5% — a 28-31× multiplier. Same $50K expenses now requires $1.5-1.6M instead of $1.25M.

The valuation adjustment

Some researchers argue that today's high stock valuations (high CAPE ratios) reduce expected returns. Wade Pfau and Michael Kitces have suggested 3.5-3.8% as more appropriate now. The conservative move: target 28-30× as your "comfortable" FI number, treat 25× as the "lean FI" floor.

How to actually use the rule

(1) Track every expense for 6 months. (2) Multiply average annual spending by 25 (or 28-30 for early retirement). (3) Subtract any guaranteed income (Social Security, pensions) — Social Security at age 67 is roughly $30K/year, equivalent to $750K of portfolio. (4) Use a compound calculator to project when your contribution rate will get you there at 7% real return.

The hidden lever: spending

Cutting $5,000 of annual expenses isn't just $5K saved — it reduces your FI number by $125K (at 25×). Conversely, lifestyle inflation of $5K/year increases the goalpost by $125K. This is why frugality compounds: every dollar of expenses you eliminate is 25 dollars of portfolio you don't need to accumulate.

The 25× rule's limits

It assumes 30 years of retirement, no major lifestyle changes, no large unplanned expenses (long-term care averages $100K+/year for some), and that historical market patterns continue. It's a planning starting point, not a guarantee. Most realistic plans target 25× as a minimum and 30-33× as comfortable.