S&P 500 Return Calculator

One pot of money compounded once a year. The rate it grows at is price growth plus the dividend yield, less the fund fee, so the three fields work together rather than one overriding the others. If dividends are reinvested more often than yearly, the yield is compounded at that frequency before it’s added, which is why quarterly reinvestment ends up slightly ahead of annual at the same yield. Contributions land throughout the year rather than all on 1 January, so a year’s deposits earn roughly half a year of growth; assuming otherwise is the most common way these projections quietly overstate things.

Contributions can run in up to three phases, so the amount can change as your life does. An employer match is a percentage of what you put in, capped, and the cap rises with inflation when your contributions are set to rise with it — a plan’s cap tracks salary, so freezing it would make the match quietly bite harder every decade.

Withdrawals can begin in a later year, and they come in three shapes. A fixed amount, a percentage of the balance, or the dividends alone. Only the last leaves the principal untouched; the other two sell from the pot to pay you, which is why they can empty it and dividends-only cannot.

Two of the switches change the method rather than the numbers. The Monte Carlo fan runs the whole projection a thousand times, with each year’s return drawn at random around your growth rate, spread by the volatility slider, then shows the tenth, fiftieth, and ninetieth percentiles instead of a single line. Where withdrawals are a fixed amount, it also reports how many of those thousand runs ran out of money. Historical mode does something different and stricter: it replays actual S&P 500 years from 1928 to 2024 in the order they happened, starting from three random years, so crashes arrive in real sequences rather than as an average.

The volatility slider only sets the width of that fan. It does not move the main projection line at all.

What the fan cannot show is that its returns are drawn each year independently and follow a bell curve. Real markets have fatter tails than that, and bad years arrive in clusters rather than politely spaced out. Historical mode is the honest test. Compounding here is annual rather than monthly, fees come off the growth rate as a flat percentage rather than as separately modelled trading costs and spreads, and the crash option is a single-year drop in a year you pick — a stress test, not a forecast.

Rates here are before inflation. Tick “Show in today’s dollars” for the real figure rather than lowering the growth rate yourself.