How compound interest works
Each month, interest is added to your balance, and next month you earn interest on that larger balance. Small differences in rate or time make a big difference at the end because the growth compounds.
This calculator compounds monthly and adds any regular monthly contribution as you go.
Example
Start with $1,000 at 5% for 10 years with no extra deposits and you'd finish with about $1,647 — roughly $647 of that is interest.