How Long Will My Retirement Savings Last?

The exact formula for how long a retirement balance lasts at a given withdrawal rate, using inflation-adjusted returns, with a worked example.

The math behind "how long will my money last" is the same annuity formula used for loan payoff timelines, just run in reverse — and it depends heavily on one number people often skip: the real, inflation-adjusted rate of return.

Step 1: Find the real rate of return

Real return = (1 + nominal return) ÷ (1 + inflation) − 1. A 6% nominal return with 3% inflation works out to roughly a 2.91% real return — the rate that matters when your withdrawal needs to keep the same purchasing power every year.

Step 2: Compare the withdrawal to real growth

If the real return alone generates more than the withdrawal every year, the balance never depletes — it holds steady or grows. This only happens at relatively low withdrawal rates relative to the real return.

Step 3: Solve for years to depletion

Otherwise, years = ln(PMT ÷ (PMT − PV × r)) ÷ ln(1 + r), where PV is the starting balance, PMT is the annual withdrawal, and r is the real return. A $1,000,000 balance withdrawing $50,000/year (5%) at a 2.91% real return works out to roughly 30.4 years.

The Retirement Withdrawal Calculator runs this instantly, or solves it backward for a safe withdrawal amount given a target number of years.