The safe withdrawal rate (SWR) is the percentage of your portfolio you can withdraw each year in retirement without running out of money. It's the engine behind every FIRE number calculation, and getting it right matters enormously. Too aggressive, and you risk depleting your savings. Too conservative, and you work years longer than necessary.
What the Trinity Study Found
In 1998, three professors at Trinity University — Philip Cooley, Carl Hubbard, and Daniel Walz — published "Retirement Savings: Choosing a Withdrawal Rate That Is Sustainable," now known simply as the Trinity Study. They analyzed U.S. market data from 1926 onward and tested every historical 30-year retirement window.
Their key finding: a portfolio of 60% stocks and 40% bonds, withdrawing 4% in year one and adjusting for inflation each subsequent year, succeeded in 96% of all historical 30-year periods. The rare failures occurred in the most severe historical sequences — retirees who had the misfortune of retiring just before major crashes.
Annual Income = Portfolio Value × Safe Withdrawal Rate
Example: $2,000,000 × 4% = $80,000/year in retirement income, adjusted for inflation annually. You increase the dollar amount each year by CPI — the percentage stays fixed at your initial 4%.
How Retirement Length Changes Your SWR
The original Trinity Study tested 30-year windows — appropriate for someone retiring at 65 and living to 95. FIRE retirees who leave work at 40 or 45 face 50-year retirements, and the math shifts meaningfully:
| Retirement Length | Retire At (Age) | Safe Withdrawal Rate | FIRE Number Multiplier |
|---|---|---|---|
| 20 years | ~75 | 4.5% | 22× |
| 25 years | ~67–70 | 4.2% | 24× |
| 30 years | ~60–65 | 4.0% | 25× |
| 35 years | ~55 | 3.7% | 27× |
| 40 years | ~50 | 3.5% | 28.5× |
| 50 years | ~40 | 3.3% | 30× |
A 40-year-old retiring today could need 50 years of portfolio support. At 3.3% SWR, a $60,000/year spending level requires $60,000 ÷ 0.033 = $1,818,000 — significantly more than the 25× ($1,500,000) figure the standard 4% rule suggests. This is why many FIRE planners in their 30s and 40s target a 3.3%–3.5% withdrawal rate and build a larger safety buffer.
Portfolio Size vs. Annual Income: The Full Picture
Here's a complete reference table showing annual income available from portfolios at different SWRs:
| Portfolio Size | At 3.3% SWR | At 3.5% SWR | At 4.0% SWR | At 4.5% SWR |
|---|---|---|---|---|
| $500,000 | $16,500 | $17,500 | $20,000 | $22,500 |
| $750,000 | $24,750 | $26,250 | $30,000 | $33,750 |
| $1,000,000 | $33,000 | $35,000 | $40,000 | $45,000 |
| $1,500,000 | $49,500 | $52,500 | $60,000 | $67,500 |
| $2,000,000 | $66,000 | $70,000 | $80,000 | $90,000 |
| $2,500,000 | $82,500 | $87,500 | $100,000 | $112,500 |
| $3,000,000 | $99,000 | $105,000 | $120,000 | $135,000 |
Sequence of Returns: The Hidden Risk
The biggest threat to any safe withdrawal strategy isn't average returns — it's sequence of returns risk. Two retirees can experience the exact same average annual return over 30 years and have drastically different outcomes, depending on when the bad years hit.
Retire in 2000 with $1,000,000? The dot-com crash in years 1–3, combined with $40,000/year withdrawals while the portfolio is down 40%, permanently impairs the portfolio. The same retiree who had a great market in years 1–5 before a crash is in a completely different position.
The full breakdown of sequence-of-returns risk — and how to protect against it — is covered in depth in our article on sequence of returns risk. The short version: cash reserves, a bond tent, and spending flexibility in early retirement are your best defenses.
A major market decline in retirement years 1–5 is far more damaging than the same decline in years 15–20. This is why early retirees should consider keeping 2–3 years of expenses in cash or short-term bonds — a withdrawal buffer that lets the equity portion recover without being sold at a loss. See also: the bridge fund strategy.
Fixed vs. Flexible Withdrawal Rates
The original SWR research assumes a fixed withdrawal: you set an amount in year one and adjust only for inflation, regardless of portfolio performance. This approach is psychologically simple but financially rigid.
Flexible withdrawal strategies — also called dynamic withdrawal strategies — allow you to spend more in good market years and pull back in bad ones. Research by Jonathan Guyton and William Klinger showed that flexible spending rules could support initial withdrawal rates up to 5–6% while still maintaining portfolio survival, because retirees give up upside in bad years.
Practical options include:
- Guardrail strategy: Increase withdrawals 10% if portfolio is up 20%+ from your initial balance; cut 10% if it drops 20%+ below. Stays within a pre-defined corridor.
- Percentage of portfolio: Always withdraw the same percentage. In a $1M portfolio at 4%, you take $40,000 year one. If it grows to $1.1M, you take $44,000 in year two. Never runs out but income fluctuates.
- Floor-and-upside: Set a minimum spending floor covered by guaranteed income (Social Security, annuity), then pull discretionary spending from the portfolio only in good years.
For most FIRE retirees, a hybrid approach works best: plan conservatively at 3.5%, allow spending to flex up by 10–15% in strong markets, and have a 2-year cash reserve to avoid selling equities in downturns. The 4% rule explainer covers the full landscape of approaches.
If you're retiring before 55, use 3.3%–3.5% as your SWR for planning purposes. Yes, this requires a larger portfolio. But it also means you're very unlikely to run out of money even in the worst historical scenarios. The extra cushion usually results in dying with substantially more wealth than you started with — which many early retirees consider a feature, not a bug, if they want to leave a legacy.
This article is for educational purposes only and does not constitute financial advice. MyFIRE is not a registered investment advisor. Always consult a qualified fee-only CFP before making retirement decisions.
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