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Safe Withdrawal Rates and the 4% Rule: What They Mean for Your Coast Number

What a safe withdrawal rate is, where the 4% rule came from, what it assumes, and how the rate you choose changes your coast number.

By J.J. Allan LLC · Published October 17, 2026 · About 10 min read

A safe withdrawal rate is the share of your portfolio you can take out in your first year of retirement, then keep taking each year with raises for inflation, with a high chance that the money lasts as long as you need it to. The best-known version is the 4% rule: withdraw 4% of your savings in year one, adjust that dollar amount for inflation every year after, and history suggests the portfolio should last at least 30 years.

The withdrawal rate sounds like something that only matters once you've retired. For Coast FIRE, it matters much earlier. It sets the size of your retirement number, and your coast number is that target pulled back to today. Choose a more cautious rate and both numbers grow. This guide explains where the 4% rule came from, what its research did and didn't show, how inflation-adjusted withdrawals work over a long retirement, and how the rate you choose moves your coast number in the Coast Clock Calculator.

The short definition

A withdrawal rate is your first year's retirement spending from savings divided by your portfolio on the day you retire. Spend $40,000 from a $1,000,000 portfolio and your withdrawal rate is 4%.

The word "safe" is doing a lot of work. It doesn't mean guaranteed. In the research behind the 4% rule, a rate is called safe or sustainable when it would have lasted through a given number of years in all, or nearly all, of the historical periods tested. It is a judgment about the past, used as a guide to the future.

Turn the definition around and you get the familiar rule of thumb for a retirement target:

Retirement number = annual spending ÷ withdrawal rate

At 4%, that is 25 times your annual spending. At 3.5%, it is about 28.6 times. At 3%, it is about 33.3 times. A small change in the rate makes a large difference to the target. (For more on that target and the FIRE movement built around it, see our guide, What Is FIRE?)

Where the 4% rule came from

1994: Bengen's historical test

In October 1994, financial planner William P. Bengen published "Determining Withdrawal Rates Using Historical Data" in the Journal of Financial Planning. He asked a practical question: if a retiree withdraws a fixed percentage of the starting portfolio in year one and then raises that dollar amount with inflation every year, what is the highest starting rate that would have survived the worst periods in U.S. market history?

Using U.S. market data from 1926 to 1992, with portfolios of large-company stocks and intermediate-term Treasury notes rebalanced each year, he tested retirements beginning in each year of the record. For a 50/50 portfolio, a first-year withdrawal of 4% followed by inflation-adjusted withdrawals never ran out in fewer than 33 years, so he concluded that 4% should be safe for a retirement of at least 30 years. He recommended holding between 50% and 75% in stocks. Retirees who started just before poor stretches, such as the mid-1960s, came closest to running out. The 4% figure was set by those worst cases, not by the average.

1998: The Trinity study

In February 1998, three professors at Trinity University in Texas, Philip L. Cooley, Carl M. Hubbard and Daniel T. Walz, published "Retirement Savings: Choosing a Withdrawal Rate That Is Sustainable" in the AAII Journal. It became known as the Trinity study.

They used U.S. data from 1926 through 1995, with the S&P 500 for stocks and long-term, high-grade corporate bonds for bonds. They tested mixes from all stocks to all bonds, withdrawal rates from 3% to 12%, and payout periods of 15, 20, 25 and 30 years, both with and without annual inflation adjustments. Rather than a single safe rate, they reported a success rate: the share of historical periods in which the portfolio still had money left at the end.

In their inflation-adjusted results, a 4% withdrawal over 30 years succeeded in roughly 95% or more of historical periods for portfolios that were at least half stocks. Success rates fell quickly at higher withdrawal rates and longer periods. The authors also stressed that choosing a withdrawal rate is a matter of planning, not a contract, and that mid-course corrections to spending would likely be needed.

What the research assumed

Both studies are widely cited, and both rest on assumptions that are easy to forget:

Why the withdrawal rate matters for Coast FIRE

Coast FIRE is about knowing when your existing savings can grow into your full retirement target without more contributions. That target comes straight from the withdrawal rate, so the rate you choose quietly shapes every other number in the plan.

There is also a timing issue. Most people choose a withdrawal rate when they are about to retire. A coaster effectively chooses one decades earlier, when they decide their coast number is "enough." If that rate later turns out to be too optimistic, the gap shows up at retirement, after years without contributions. Picking a rate you are comfortable with, and testing a more cautious one, is part of deciding when to stop saving.

How inflation-adjusted withdrawals work

The 4% rule is often misread as "spend 4% of whatever the portfolio is worth each year." That is a different strategy. Under the rule as studied, only the first year's amount is set by the percentage. After that, the dollar amount simply rises with inflation, whatever the markets do.

A worked example (illustrative only)

Imagine you retire with $1,000,000 and withdraw 4%, or $40,000, in year one. Prices then rise 3% a year. Your withdrawals in actual dollars would be about:

Over 30 years, that adds up to about $1.9 million in actual dollars, but every one of those withdrawals buys what $40,000 buys today. In today's dollars, you are spending the same $40,000 every year. (For more on how rising prices change long-range numbers, see our guide, Inflation and Your Coast Number.)

Whether the money lasts depends on returns. If the portfolio earned a perfectly steady 7% a year with 3% inflation, a real return of about 3.9%, and you took each year's withdrawal at the start of the year, you would still have about $850,000 in today's dollars after 30 years. Markets are not steady, though, and the order of the returns matters as much as their average.

Sequence-of-returns risk

Take the same $1,000,000 and the same inflation-adjusted $40,000 withdrawals, and give the portfolio two 30-year return paths with exactly the same average real return as the steady case. The only difference is when the bad years happen:

Same average return, same spending, an outcome more than six times better. Early losses hurt more because withdrawals are taken from a shrinking balance, and the money sold at low prices isn't there to recover. This is the risk the 4% rule's worst-case periods were capturing, and it is the main reason a safe rate is lower than the average return alone would suggest.

These figures are illustrative, not projections or recommendations. The return paths are simplified examples we constructed to show the effect of timing, not historical data.

The trade-off: lower rate, bigger coast number

A lower withdrawal rate makes a plan more resilient, but it also raises the bar. A bigger retirement number means a bigger coast number today and a later coast age.

Here is what that looks like in the Coast Clock Calculator with its starting values: a 30-year-old with $70,000 take-home pay, $40,000 a year in spending, $100,000 invested, retiring at 65, with a 7% expected return and 3% inflation. Only the withdrawal rate changes:

Moving from 4% to 3% raises the coast number by about a third and pushes the coast age out roughly four years. That is the price of a larger safety margin, and whether it's worth paying depends on how long your retirement might last and how flexible your spending is.

How the Coast Clock Calculator uses the withdrawal rate

The calculator has a Withdrawal rate slider under Advanced assumptions. It starts at 4% and ranges from 2.5% to 6% in quarter-point steps. Here is exactly what it does:

If you have already reached your retirement age, the calculator checks whether your savings cover your retirement number at the rate you chose.

Practical considerations

Flexibility is worth a lot. The 4% rule assumes spending never adjusts. Being willing to trim spending after a bad year, even modestly, can make a portfolio far more durable. Many people treat 4% as a starting point to revisit, not a fixed paycheck.

Guardrails formalize that flexibility. Guardrail approaches set upper and lower bounds around your withdrawals. If markets fall far enough that your current withdrawal becomes too large a share of the portfolio, you cut spending by a set amount; if markets rise enough, you give yourself a raise. The best-known version comes from Jonathan Guyton and William Klinger, whose 2006 Journal of Financial Planning paper tested such decision rules over 40-year periods and found they supported higher starting withdrawal rates, in exchange for spending that varies from year to year.

Longer horizons call for more caution. An early retiree may need savings to last 40, 50 or even 60 years, well beyond the 30-year periods the original studies tested. Later research, including Karsten Jeske's long-running safe withdrawal rate series on Early Retirement Now, generally finds that longer retirements call for starting rates somewhat below 4%, especially when markets are expensive at the start. In our sequence example above, a portfolio that survives 30 years runs dry in year 36.

Sequence risk is greatest at the start. The first five to ten years of retirement carry the most weight. Some retirees hold a cash or bond cushion for those years, or plan to keep a little income coming in, so they don't have to sell stocks after a crash.

Social Security and other income lower what savings must cover. Social Security, a pension or part-time work reduce how much your portfolio needs to supply. The calculator doesn't model these separately yet and assumes your investments cover all of your retirement spending, which is the cautious version. Social Security benefits also depend on when you claim; claiming before full retirement age permanently reduces the monthly amount.

Common misconceptions

"The 4% rule guarantees my money will last." It doesn't. It describes what would have worked in past U.S. markets over 30 years. The future may be better or worse.

"4% means I spend 4% of my balance every year." Under the rule as studied, 4% sets only the first year. After that, withdrawals rise with inflation regardless of the balance.

"A lower rate is always better." A lower rate is safer, but it means more years of saving. A rate that is too cautious can mean working longer than you need to and often leaves a large unspent balance.

The bottom line

The 4% rule is a useful starting point drawn from careful historical research, built for 30-year retirements with a solid stock allocation. It is not a guarantee, and longer early retirements, rigid spending and a weak start in the markets all argue for some caution.

For Coast FIRE, the withdrawal rate is more than a retirement-day decision. It sets your retirement number and, through it, how much you need invested today. To see how much your own plan depends on it, visit Coast Clock or go straight to the Coast Clock Calculator, open Advanced assumptions and try the withdrawal rate at 3.5% and 3% alongside the default 4%.

Further reading

For a first-hand account of planning withdrawals for a much longer retirement than the original studies assumed, Kristy Shen and Bryce Leung's Quit Like a Millionaire tells how the couple saved aggressively, retired in their early thirties and handled the practical questions that follow, from withdrawal rates to market downturns.

J.L. Collins's The Simple Path to Wealth makes a plain-spoken case for simple, low-cost index fund investing, and it includes a discussion of withdrawal rates and how much you can spend from a portfolio in retirement.

And because the hardest part of any withdrawal plan is staying flexible when markets fall, Morgan Housel's The Psychology of Money is worth reading alongside them. Its short chapters cover risk, room for error and knowing when you have enough.

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This article is for general education only and is not financial, tax or legal advice. Withdrawal rates, returns and tax rules vary, and past market performance doesn't guarantee future results. For decisions about your own money, consult a licensed financial professional.

Sources

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