Compound Interest Calculator
Compounding is growth earning growth. This calculator shows how a starting balance plus regular contributions can build over time, and how much of the final number comes from your deposits versus growth.
Ending balance
- Total contributions
- Estimated growth
Enter your numbers above to see an estimate.
How this works
The calculator converts your annual rate into an effective rate based on how often interest compounds, then grows your starting balance and each contribution forward to the end of the term. Earlier dollars have more time to compound, which is why starting sooner matters so much.
Contributions are assumed to be added at the end of each period. A 0% return simply sums your starting amount and contributions, with no growth.
What this does not include
Returns here are a smooth, constant estimate. Real investments rise and fall, sometimes sharply, and a constant rate can overstate how steady the path is.
It excludes taxes, fund fees, and inflation, each of which reduces what your ending balance is actually worth. Use it to understand the shape of compounding, not as a guaranteed forecast.
A quick example, and how to read it
Leave the numbers as they load: $5,000 to start, $250 a month, 7% a year, for 25 years. Now watch the two figures on the right. Early on, almost everything you see is money you put in. Somewhere in the later years the estimated growth quietly passes your total contributions, and from then on your money is doing more of the work than you are.
That crossover is the whole point of compounding, and it's why starting earlier usually beats saving more later. Try it: keep the same monthly amount but set the years to 35 instead of 25, and notice how much the ending balance jumps from those ten extra years alone.
For where this fits in the bigger picture, see personal finance basics. If you're aiming at a specific number instead, the time value of money calculator works the same math backward from a goal.