S&P 500 Historical Returns Calculator

Backtest any monthly investing plan against more than 150 years of U.S. stock market history, including inflation-adjusted results.

What this calculator tests

Choose a monthly contribution, investment window, and starting assumptions, then compare every possible historical start date in Robert Shiller's S&P 500 dataset.

The tool reports median, best, and worst outcomes so you can see the range of real historical results instead of relying on a single average return.

Why it matters

The same investing plan can feel very different depending on whether it begins before a boom, a crash, inflation, or a long sideways period.

This page helps beginner investors understand long-term risk, sequence of returns, nominal dollars, and inflation-adjusted purchasing power before committing to a plan.