How the “How Long Will My Money Last” Calculator Works
We believe a calculator you can't see inside isn't worth trusting. Here's exactly how this one works.
The two phases
The calculator models your money in two stages. During the accumulation phase (from your current age to your retirement age), your savings grow at the assumed return rate with no withdrawals. During the distribution phase (from retirement onward), each year your balance earns the return rate, and your withdrawal — adjusted upward for inflation — is taken out. We repeat this year by year until the balance reaches zero (the depletion age) or you reach age 120.
Inflation is built in
Your withdrawal amount grows every year with inflation, because $3,000 a month today won't buy the same in twenty years. Many free calculators skip this and overstate how long your money lasts. We don't.
Three scenarios, not one false number
Markets don't deliver the same return every year, so we show three: a conservative case, your expected case, and an optimistic case. The real future usually lands somewhere in between — seeing the range is more honest than a single figure.
The market-volatility stress test
Because even the three scenarios assume steady returns, we also run a Monte Carlo simulation: 1,000 randomized sequences of good and bad market years, to estimate the probability your money lasts to a target age. This captures something a single projection can't — the risk that a market downturn early in retirement does outsized damage.
What we don't model
These tools don't account for taxes, healthcare costs, changes in your spending, or guaranteed-income products like annuities. They're a starting point for understanding, not a complete financial plan. For that, talk to a licensed professional.
MoneyPlanCalc provides educational tools only and is not a registered investment advisor.