Compound Interest Calculator
See how savings grow with interest and regular contributions.
Year-by-year breakdown
| Year | Start | Contributions | Interest | End balance |
|---|
Estimates only, for general information. Figures assume a constant rate and exclude tax and fees.
How compound interest works
Compound interest is interest earned on both your original money and on the interest it has already earned. Because each period builds on a slightly larger balance, savings grow faster over time — the effect is strongest over long horizons.
The formula
For a lump sum with no further contributions, the future balance is:
A = P (1 + r / n)n t
| A | Final balance |
|---|---|
| P | Principal (initial deposit) |
| r | Annual interest rate (as a decimal) |
| n | Number of times interest compounds per year |
| t | Time in years |
When you add regular contributions, this calculator also adds the growth of each deposit from the date it is made, and lets you choose whether deposits land at the start or end of each period.
Tips
Starting earlier usually matters more than starting bigger: even small regular contributions compound substantially over decades. More frequent compounding raises the effective yield slightly, which the calculator reports as the effective APY.
Invest $10,000 at 5% compounded monthly for 10 years while adding $200 a month. The balance grows to about $47,527 — roughly $34,000 of that is your own money ($10,000 plus $24,000 of contributions) and around $13,527 is interest earned.
Why compounding rewards patience
The longer your money compounds, the more of the final balance comes from growth rather than from your own deposits. In a long savings plan the interest can eventually add more each year than you contribute — which is why starting earlier often matters more than saving a larger amount later on.
Make the most of it
- Start sooner. A few extra years invested can outweigh a bigger monthly contribution begun later.
- Contribute regularly. Every deposit begins compounding from the day it lands, so steady investing adds up.
- Leave it to grow. Withdrawing interrupts compounding and resets much of the benefit.
Real-world returns rise and fall from year to year; this tool assumes a steady rate, so treat the result as a projection rather than a promise.