Compound interest calculator
FinanceNo. 15 / 84
See what a starting sum plus monthly contributions becomes, with monthly, quarterly or annual compounding and a year-by-year table.
compounding is interest doing push-ups while you sleep. it just takes years.
work surface
Math, not advice — results are indicative.Read the disclaimer.
most-used utilities
Retirement sketch
200 a month from 30 to 65 at 7%, which is either motivating or a reason to sit down.
Emergency fund
6,000 saved plus 100 a month at 3% — slow, safe and still better than the drawer.
Late start
Starting at 45 instead of 30 costs more, and the widget will show exactly how much.
pro tips
The first years look flat. Almost all the growth arrives late, which is why quitting at year four feels reasonable and costs the most.
Start ten years earlier and the same monthly contribution can more than double by retirement. The last decade has the fewest years and the biggest balance.
Match the compounding setting to the account: monthly for most savings, quarterly for some certificates, annual for whatever the brochure promised.
what it does
Enter what you have now, what you add each month, the annual rate you expect and how long you can leave it alone. The widget compounds month by month at the frequency you pick, then shows the final balance, the money you put in and the interest that turned up on its own.
Useful for retirement sketches, a child's savings account, an emergency fund you are slowly building, or the annual argument about whether the index fund is worth the wait. Pick monthly, quarterly or annual compounding to match the fine print on the account.
Start with 5,000, add 200 a month at 7% for ten years. Monthly compounding ends at about 44,665. You contributed 29,000, so roughly 15,665 is interest. Annual compounding lands near 44,046 for the same plan — the frequency is a small detail until it is not.
Contributions are added at the end of each month, and the rate is treated as a nominal annual rate compounded at the frequency you choose. Taxes, fund fees and inflation are not included, and no investment has ever delivered a steady 7% just because a calculator said so.
quick answers
What does compounding frequency change?
How often interest is added to the balance. Monthly compounding earns a little more than annual at the same nominal rate, because the interest starts earning interest sooner.
Are contributions added at the start or the end of the month?
The end. Each month the balance earns interest first, then your contribution lands. Adding it at the start would produce a slightly higher balance.
Does this include taxes, fees or inflation?
No. It shows growth before tax, before fund fees and with inflation ignored. Treat the result as a sketch, not a promise.