Compound interest

This tool pairs with "Why bother investing at all". The question it answers is the plainest one in finance: a sum of money, a yearly return, a number of years — what does it grow into? Click a preset, then drag the return and the years separately, and watch which of the two moves the result more. That comparison is the whole argument of the article.

Result

At an assumed 6% yearly return, 10,000 becomes about 32,071 after 20 years, including 22,071 of growth; by the rule of 72, doubling takes roughly 12.0 years.

Ending value: 32,071
Growth: 22,071
Rule-of-72 doubling time: 12.0 years

Chart: compound ending value over time, with the starting amount shown as the dashed line. Hold and drag across the chart, or use arrow keys, to read point by point.

The yearly return is an assumption. Real paths wobble and can be negative. Not investment advice.

Assumptions & limits

The curve assumes the same return arrives every single year, and real markets never pay that way: this is an order-of-magnitude reference, not a path, and certainly not a promise. The higher you drag the return, the harder you should ask where such a number would come from. Broad stock markets have historically returned high single digits over long stretches; inputs above that are wishes, not plans.