How Compound Interest Changes Savings Over Time

Compound growth earns a return on the starting balance and, over time, on prior growth. The result depends on the amount invested, contributions, rate, compounding and the length of time the money remains invested.

Time can matter as much as the rate

Compounding needs time. A small difference in years can create a large difference in the ending balance because later periods build on a larger base. This is why two people contributing the same amount can end with different results when one starts earlier.

Contributions and investment return are separate drivers

The ending balance includes money you contributed and growth produced by the assumed rate. Keep those pieces separate when reading the result. A high ending balance is not all investment gain if regular contributions make up a large part of it.

An assumed rate is not a guaranteed rate

Investment return estimates are assumptions. Actual returns can be uneven, negative in some periods, and affected by fees or taxes. Savings products may have stated rates that can change over time. Test more than one rate instead of treating a single estimate as certain.

Compounding frequency has an effect

When the stated rate is the same, more frequent compounding can slightly increase the effective growth because interest is credited sooner. The effect may be small compared with the difference created by time, contribution size or a materially different rate.

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Investment and savings results are estimates and do not predict future performance. Account fees, taxes, withdrawals and changing rates can affect actual results.