How Much Do You Need to Retire?

The 4% rule: where it came from and what it actually means

William Bengen was a financial planner who got tired of guessing. In 1994, he pulled 75 years of stock and bond market data and ran every possible 30-year retirement scenario starting from 1926 onward. His question: what withdrawal rate never failed? The answer was 4.15%, which he rounded to 4%.

The math is simple. Withdraw 4% of your portfolio in year one, increase it by inflation each year after that, and a 50/50 stock-bond portfolio survived every 30-year window in the historical record. Including the Great Depression. Including the stagflation of the 1970s. Including the dot-com crash.

The inverse gives you the retirement number: divide annual withdrawal needs by 0.04, or equivalently multiply by 25. Need $60,000 from your portfolio each year? You need $1,500,000. Need only $20,000 because your pension covers the rest? You need $500,000.

Bengen later updated his research to suggest 4.5% or even 4.7% is defensible with a better asset allocation. But 4% became the standard because it has the most historical evidence behind it and gives you a margin of safety. Most people planning a retirement longer than 30 years use 3.5% or 3% to be conservative, which this calculator shows as the 28x and 33x multiples.

Why pension income is so valuable in this math

The number that shocks most people: every $1,000 per month of pension income reduces your required portfolio by $300,000. That's not a figure pulled from anywhere dramatic. It's straight arithmetic. $1,000/month is $12,000/year. $12,000 times 25 is $300,000.

A teacher retiring with a $3,500/month pension effectively walks into retirement with a $1,050,000 phantom portfolio. It doesn't show up in any account balance. It doesn't fluctuate with markets. It doesn't require a withdrawal strategy. It just pays every month until death, and in many systems, it continues to a surviving spouse at a reduced rate.

This is why the comparison between a pension and a 401(k) is so often misunderstood. The pension isn't just income. It's a substitute for a very large portfolio that you never had to accumulate. The federal employee with a $2,500/month FERS pension and a $300,000 TSP balance is in a better position than many private-sector workers with a $700,000 401(k) and no guaranteed income, depending on spending levels.

The calculator shows you the exact portfolio value your guaranteed income offsets. That figure is real. Treat it as such when evaluating your retirement readiness.

Sequence of returns risk, and why pensions sidestep it

There's a risk in retirement that most accumulation-phase calculators ignore: sequence of returns. It doesn't matter what your portfolio averages over 30 years if it drops 40% in years one and two. A $1,000,000 portfolio losing 40% immediately becomes $600,000. You're now withdrawing from a permanently smaller base, and most of the academic research shows you never fully recover the compounding you lost in those early years.

This is why "average returns" can be dangerously misleading. Two retirees with identical 7% average returns over 30 years can have wildly different outcomes based on the order returns arrived. The one who got the bad years first runs out of money. The one who got the good years first has money left over.

A pension eliminates this risk for the income it covers. The pension payment in year one of a market crash is identical to the payment in year one of a bull run. The sequencing is irrelevant because there's no portfolio draw. Every dollar your pension covers is a dollar your portfolio doesn't need to provide during a downturn, which directly reduces your sequence-of-returns exposure.

Social Security works the same way. Delaying Social Security from 62 to 70 increases the monthly benefit by roughly 77%, and that increase represents guaranteed income that protects your portfolio from early sequence-of-returns damage during the years you'd otherwise be drawing it down most aggressively.

Inflation and the real retirement number

The 4% rule accounts for inflation by increasing withdrawals each year. But the starting spending figure matters enormously. $80,000 per year today is not $80,000 per year in 15 years if inflation runs at 3% annually. At 3% compound inflation, $80,000 today becomes about $124,000 in 15 years. Your retirement number should be calculated on your inflation-adjusted spending at the time you retire, not your spending today.

This calculator adjusts your spending forward to retirement date using the inflation rate you enter. That's why the projected retirement number sometimes surprises people: it's in future dollars, not today's purchasing power. The gap looks larger. It is larger, in nominal terms. But if your portfolio also grows in nominal terms, the math works out. What you're really testing is whether your real (inflation-adjusted) return is sufficient.

Pensions with cost-of-living adjustments (COLAs) protect against this. A pension that increases 2% per year alongside 3% inflation still loses 1% of purchasing power annually, but far less than a fixed pension that provides the same nominal dollar every year for 30 years. Check whether your pension includes a COLA and factor that into your long-term income projections.