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Retirement fails on arithmetic, not vibes.
The 4% rule (Trinity study) says withdrawing 4% of your starting portfolio, adjusted for inflation, survived nearly every 30-year window in market history. This calculator stress-tests the rule with your own numbers: portfolio size, withdrawal rate, assumed return, and inflation — and tells you the exact year the money runs out if it does.
Near-retirees use it to turn a portfolio balance into an income number, and FIRE planners use it to test 40-year horizons at 3.5%. It answers the only question that matters: what can I spend without the money dying first?
For 30-year retirements, historically yes — it survived every window including the Depression, though 1966 retirees came close to failing. For 40+ year early retirements, 3.25–3.5% is the safer researched floor. The rule assumes a diversified stock/bond portfolio; 100% cash or 100% crypto breaks the premise.
Average return does not determine survival — the ORDER of returns does. A 30% crash in year 2 of retirement while withdrawing is far deadlier than the same crash in year 20. This calculator uses constant returns, so it shows the average case; real planning adds a bad-first-decade stress test. That's the guardrail answer: flexible spending.
Three levers: start lower (3.5% instead of 4%), hold 1–2 years of spending in cash so crashes don't force selling at the bottom, and build in flexibility — committing to skip inflation raises after down years historically rescues most failing scenarios. A part-time income of even $1,000/month in early retirement moves the math dramatically.