The 4% rule: how much do you actually need to retire?

If you can spend 4% of your portfolio in year one and adjust for inflation afterward, your money should last 30 years. That's the "4% rule" — born from a single 1998 study, controversial ever since, and still the closest thing to a universal answer to "what's my retirement number?"

Where the 4% came from

In 1998, three professors at Trinity University (Cooley, Hubbard, and Walz) published Retirement Savings: Choosing a Withdrawal Rate That Is Sustainable. They simulated retirement portfolios against actual US market history (1926–1995), testing various initial withdrawal rates and portfolio mixes against a 30-year retirement.

Their question was simple: if you retire with $X and pull out a fixed amount every year (adjusted for inflation), what's the chance you run out before 30 years?

Their headline finding: a portfolio of 50% stocks / 50% bonds, starting with a 4% withdrawal rate (and adjusting that dollar amount up for inflation each year), survived 95–100% of historical 30-year windows. That's the "4% rule."

The math, simply

The 4% rule means your "retirement number" is roughly 25× your annual spending:

Some examples:

• $40k/year spending → $1,000,000 target
• $60k/year spending → $1,500,000 target
• $100k/year spending → $2,500,000 target

Note: this is spending, not income. Pre-retirement, you needed gross income to cover spending + taxes + savings. Retired, you only need to fund spending (plus some taxes on withdrawals, depending on account type).

The big asterisks

The original Trinity Study is 25+ years old, and the consensus in 2025 is: "4% is probably still fine, but it's a rule of thumb, not a guarantee."

It assumes US market history continues. The 4% rate survives 95% of historical 30-year periods. But US markets had an extraordinarily good century. Apply the same methodology to Japanese markets and the safe rate drops to ~1–2%. If the next 30 years look like any of the worse-than-US developed markets, 4% could be too aggressive.

It assumes a 30-year retirement. Someone retiring at 60 has a 30-year horizon. Someone retiring at 45 (FIRE) needs to last 50+ years. Updated studies suggest 3.3–3.5% for 50-year horizons. That changes the target multiplier from 25× to ~28–30×.

It assumes fixed real spending. Real retirees don't actually spend a flat inflation-adjusted amount. Most retirees underspend in the early years (energetic but cautious), overspend in middle retirement (peak travel + medical), and underspend at the end. Dynamic strategies (Guyton-Klinger, Variable Percentage Withdrawal) outperform fixed 4% on the same portfolios.

It assumes a US dollar-denominated retirement. If you're planning to retire abroad in a lower-cost-of-living country, your effective withdrawal rate is much lower.

Worked example: build your target

Steps:

1. Estimate annual spending in retirement. Not income — spending. Look at your last 12 months' actual spending. Subtract anything that'll disappear (mortgage if you'll have paid it off, college savings, kids-related costs). Add anything that'll grow (healthcare, travel).
2. Multiply by 25. That's your nominal target.
3. Adjust for retirement horizon. 30 years → 25×. 40 years → 28×. 50 years → 30×.
4. Adjust for risk tolerance. If "95% historical success" isn't comfortable, target 3.5% instead of 4% → multiplier becomes 28×.

Example: 45 years old, current spending $60k/year, want a 40-year retirement at modest confidence.

• Annual spending: $60,000
• Horizon: 40 years → 28× multiplier
• Target: $60,000 × 28 = $1,680,000

The strongest critique of the 4% rule

Wade Pfau and others have argued the 4% rule is dangerous because it implies false precision. "4% is safe" sounds like a guarantee. It's not — it's "95% historical."

The 5% failure cases are interesting. They all share a common feature: a major bear market in the first 5–10 years of retirement. The portfolio shrinks fast, and the fixed withdrawal becomes a larger and larger percentage of a shrinking pot. Retirees who hit a "sequence-of-returns" disaster don't recover even if markets bounce back later.

The defensive moves:

• Cash buffer. Keep 2–3 years of spending in cash. Use it during downturns instead of selling stocks at the bottom.
• Dynamic withdrawals. Cut spending in down years, raise it in good ones. Even modest flexibility raises safe withdrawal rates significantly.
• "Just one more year." Working 1–2 extra years before retirement has an outsized effect — you both add to the portfolio and reduce the years it needs to last.

The takeaway

The 4% rule is a useful starting point, not a finishing answer. Most planners use it to estimate the rough target, then refine with stress tests:

• Could the portfolio survive a 1970s-style stagflation in the first decade?
• Are healthcare costs modeled realistically?
• What happens if Social Security pays 80% instead of 100%?
• Is there a part-time income option that lets you adjust if markets disappoint early?

The simple version of the rule — multiply spending by 25, you're done — gets you to the right zip code. The neighborhood requires more work.