What is Compounding?

Compounding is what happens when the money an investment earns starts earning money of its own. In the first year, growth comes only from the amount originally invested. In the second year, it comes from that amount plus the first year's gains, and so on. The gains pile on top of earlier gains, so the total grows faster over time, like a snowball picking up more snow as it rolls. For compounding to work, the earnings have to stay invested. That means leaving interest in the account, or using dividends (cash payments companies make to shareholders) to buy more shares.

Say you invest $10,000 and, as a purely hypothetical illustration, it grows by 10% every year. After year one it is worth $10,000 × 1.10 = $11,000. In year two the 10% applies to $11,000, adding $1,100 rather than $1,000, for $12,100. In year three it adds $1,210, for $13,310. Continue for 30 years and the result is $10,000 multiplied by 1.10 thirty times, roughly $174,500. If each year's gain had been taken out instead of reinvested, the investment would have produced $1,000 a year. After 30 years that is the original $10,000 plus 30 × $1,000, or $40,000 in total. The difference of about $134,500 comes entirely from returns earning returns.

Compounding works in both directions, and real returns do not arrive in neat, steady steps. Losses compound too: a 50% loss needs a 100% gain to recover, and an 80% loss needs 400%. This is why an average of yearly returns can mislead. An investment that rises 50% one year and falls 50% the next has an average return of 0%, yet $10,000 becomes $15,000 and then $7,500. The compound annual growth rate, or CAGR, is the steady yearly rate that would have produced the same end result, and it gives a more honest picture. Costs compound as well. An annual fee of 1% removes a slice every year, and that missing money no longer earns anything.

For a private investor building a long-term portfolio, compounding explains why time often matters more than the starting amount. It also explains why reinvesting dividends, keeping fees low and avoiding deep losses carry so much weight. As a reference point, the S&P 500 returned 10.2% a year over 30 years to June 2026 with dividends reinvested. Past returns say nothing certain about the future, but the arithmetic of compounding holds at any rate of return.

By Dr. Harry Hamann

What is the difference between compounding and compound interest?
Compound interest is compounding applied to interest, for example on a savings account or bond. Compounding is the broader idea: any reinvested return, including dividends and price gains, starts producing returns of its own.

What is the rule of 72?
It is a rough shortcut for estimating how long money takes to double. Divide 72 by the yearly return. At a hypothetical 8% a year, money doubles in about 9 years. At 6%, it takes about 12 years.

Do losses compound too?
Yes. Each loss shrinks the base that future gains build on, so recovery takes a larger percentage gain than the loss itself. A 50% loss needs a 100% gain to get back to the starting value.