Play · uncertainty & withdrawal rates
Retirement Range Simulator
Updated 2026-07-27 · Concept: sequence risk: why the honest answer is a range
Most retirement calculators ask for a return, then draw one confident line. Real markets do not hand out an average; they hand out a sequence, and the order matters enormously. This tool runs your numbers five hundred times, drawing each year's return at random, and shows what came back: not a promise, but a fan of futures (a good tenth, a bad tenth, and the middle). The width of that fan is the true answer.
Predict first
$300,000 saved, spending $40,000 a year: in how many futures out of 100 does the money last 30 years?
Pick an estimate, or skip to your own numbers.
Futures in which the money outlasts the years
n/a
A teaching model of uncertainty, not a forecast. Assumptions, plainly: each year's real (after-inflation) return is drawn independently from a normal distribution with a mean of 5% and a standard deviation of 12%; spending is withdrawn at the start of each year and held constant in today's dollars; there are no taxes, fees, pensions, Social Security, part-time work, inheritances, or the very human ability to spend less in a bad year. Two of those assumptions are known to be wrong: real returns are not normally distributed, and real years are not independent of one another. For long-run return context see the SEC's investor.gov on stocks; for where the 4% rule comes from, Cooley, Hubbard and Walz, “Sustainable Withdrawal Rates From Your Retirement Portfolio,” Financial Counseling and Planning 10(1), 1999 (the “Trinity study”), which tested historical sequences rather than random ones and found roughly 4% survivable over 30 years. Five hundred runs is enough to see the shape and not enough to pin the last percentage point; press “Run 500 more futures” and watch the number wobble. Teaching only; not personalised financial advice.
Go to now, ye that say, To day or to morrow we will go into such a city, and continue there a year, and buy and sell, and get gain: Whereas ye know not what shall be on the morrow… For that ye ought to say, If the Lord will, we shall live, and do this, or that.James 4:13-15
KJV. James is not against planning; he is against the sentence that leaves God out of it. The omitted clause is his reason: 'For what is your life? It is even a vapour, that appeareth for a little time, and then vanisheth away.' A range instead of a promise is what that humility looks like in arithmetic.