Compound growth, and the cost of waiting
What a monthly amount could become, under assumptions taken from the historical record rather than a round number, and what starting later costs. Everything is in today's dollars.
Your plan
A monthly amount is enough. The horizon and delay are choices, not facts about you. Estimates are fine.
Your numbers never leave this page. They are not saved, sent, or tracked. The only thing loaded is the public historical dataset.
What you will get
A projected value under a cautious and a middle assumption, both drawn from the rolling-period record below, next to the no-growth case. A chart and a year-by-year table. What the same plan started later ends at. Then one next move.
Where the assumptions come from
The U.S. stock market, 1871 to the last complete month of the dataset, with dividends reinvested and inflation removed. Every calendar month is a start date, so nothing is cherry-picked. The "cautious" assumption is the return one in ten historical periods of your horizon fell below; "middle" is the median.
Loading the historical record…
Historically, diversified long-term investing has rewarded patience, but outcomes are uncertain and losses can occur. The market does not "always return" a percentage; the table shows how wide the range has been.
Source and method
- Robert J. Shiller, U.S. Stock Markets 1871–Present and CAPE Ratio, monthly S&P composite price, dividends and CPI (econ.yale.edu/~shiller/data.htm), via the datahub.io/core/s-and-p-500 mirror. Coverage and retrieval date are printed with the table above.
- Total return assumes dividends are reinvested monthly at one twelfth of the annual rate. Real figures divide by the CPI. Rolling returns are annualised. The projection compounds monthly and treats your contribution as constant in today's dollars.
- A broad U.S. index is used as the historical example because it has the longest clean record; a diversified portfolio may differ, and fees and taxes are not included.