Portfolio longevity is a race between two forces: the return your savings earn and the withdrawals you take out. Because withdrawals must rise with inflation just to buy the same groceries each year, while returns are uncertain, the answer is never simply "portfolio ÷ spending."

This calculator models the drawdown year by year, using the conventional sequence:

Worked example. A $750,000 portfolio, $60,000/year of spending, a 6% return and 3% inflation, no Social Security:

Notice the trap in the first year: the balance actually grew from $750,000 to $731,400 after a $60,000 withdrawal — returns nearly covered the draw. That early illusion of sustainability is why an 8% initial withdrawal rate still looks fine for several years before the inflation-adjusted withdrawals overtake the returns. The Safe Withdrawal Rate calculator tests the same portfolio against the 4% benchmark, and our guide to the 4% rule walks through the research behind it.

One important limitation: this model applies a steady average return every year. Real markets do not. See the sequence-of-returns section below for why that matters, and treat the output as a planning estimate rather than a forecast.

A systematic withdrawal plan (SWP) takes a fixed, scheduled amount from your portfolio — monthly or annually — rather than selling assets ad hoc. It's the default structure for most retirement income, and the strategy this calculator models.

The critical design choice is whether withdrawals are fixed in nominal dollars or inflation-adjusted. The difference compounds dramatically:

Two lessons fall out of that table. First, indexing withdrawals to inflation costs roughly six years of portfolio life — but not indexing them means accepting a steadily falling standard of living, since $60,000 buys about 55% as much after 20 years at 3% inflation. Second, the relationship between spending and longevity is highly non-linear: cutting the draw by 25% (from $60,000 to $45,000) added about seven years, and halving it to $30,000 nearly tripled the portfolio's life to roughly 42 years.

That non-linearity is the single most useful fact in retirement planning. Small, permanent spending reductions — or a couple of extra working years, which both add to the portfolio and shorten the drawdown — move the depletion date far more than chasing an extra percentage point of return.

Two inputs change the answer more than most people expect.

Social Security. Every dollar of benefit is a dollar you don't withdraw. Because the Social Security Administration applies an annual cost-of-living adjustment (COLA), the benefit rises with inflation alongside your spending — so it keeps pace rather than eroding. A $2,000/month benefit against $60,000 of spending cuts the portfolio draw from $60,000 to $36,000, which in the example above extends the portfolio from about 15 years to roughly 31 — from age 80 to age 96. Delaying a claim also raises the benefit permanently: benefits grow by about 8% per year of delay up to age 70. You can estimate your own figure with our Social Security calculator, then verify it against your official earnings record at ssa.gov/myaccount.

Taxes. Withdrawals from a traditional 401(k) or IRA are taxed as ordinary income, per IRS Publication 590-B. To spend $60,000 at a 15% effective rate you must withdraw about $70,600 — a 17.6% larger draw than the headline number:

Set the tax rate to 0% if your savings sit in a Roth account, where qualified distributions are tax-free, or if you're modelling spending in after-tax terms already. Note also that traditional accounts carry required minimum distributions beginning at age 73, which can force withdrawals larger than your spending need. The Roth vs Traditional comparison covers the trade-off in depth.

This calculator — like nearly every drawdown calculator — applies your expected return evenly, every year. Markets don't cooperate. The order in which returns arrive matters enormously once you're withdrawing, a hazard known as sequence-of-returns risk.

Consider two retirees with identical portfolios, identical withdrawals, and the identical average return over 30 years. The one who happens to retire into a severe bear market sells shares at depressed prices to fund early withdrawals, permanently shrinking the base that later recovery can compound. The one who gets good early years may never run out. Same average, different outcomes.

This is precisely why the withdrawal-rate literature exists. Bill Bengen's 1994 study and the subsequent Trinity Study tested withdrawal rates against actual historical market sequences rather than averages, and arrived at roughly 4% as the rate that survived the worst historical 30-year windows. A straight-average model like this one will always look more optimistic than that research.

How to use this calculator responsibly:

• Stress-test the return. Run your numbers at 6%, then again at 4% and 3%. If the plan only works at 7%, it isn't a plan.
• Check your first-year withdrawal rate. If it's meaningfully above 4%, the historical research suggests elevated depletion risk regardless of what the average-return model shows.
• Plan to a longer horizon than you expect. Per the Social Security Administration's actuarial data, a 65-year-old today has a substantial chance of living past 90 — and roughly one in seven men and one in five women reach 95. Planning to age 95 is common practice.
• Keep a cash buffer. One to two years of spending in cash or short-term bonds lets you avoid selling equities during a downturn — the direct defence against sequence risk.

For an early-retirement horizon of 40+ years rather than a standard 30, the same risks compound further; our FIRE calculator and the FIRE roadmap guide address that longer window. This tool is for educational and planning purposes and is not investment or tax advice — for a decision this consequential and permanent, confirming your assumptions with a fee-only fiduciary advisor is worth the cost.