Compound Interest Calculator
What a balance grows to over time, with or without regular contributions, and how much of it is interest.
Runs entirely in your browser. Nothing is uploaded, logged or stored.
Balance at the end
17,175.24
- Total paid in
- 13,000.00
- Interest earned
- 4,175.24
- Effective annual rate
- 5.12 %
Year by year
| Year | Paid in | Interest | Balance |
|---|---|---|---|
| 1 | 2,200.00 | 79.05 | 2,279.05 |
| 2 | 3,400.00 | 223.53 | 3,623.53 |
| 3 | 4,600.00 | 436.81 | 5,036.81 |
| 4 | 5,800.00 | 722.38 | 6,522.38 |
| 5 | 7,000.00 | 1,083.97 | 8,083.97 |
| 6 | 8,200.00 | 1,525.44 | 9,725.44 |
| 7 | 9,400.00 | 2,050.90 | 11,450.90 |
| 8 | 10,600.00 | 2,664.64 | 13,264.64 |
| 9 | 11,800.00 | 3,371.17 | 15,171.17 |
| 10 | 13,000.00 | 4,175.24 | 17,175.24 |
Interest on interest is the whole point, and it is slow before it is fast. The year-by-year table shows the crossover: the year where the interest earned starts to outgrow what you paid in.
How it works
The balance is multiplied by one plus the periodic rate at every compounding period, and any contribution is added at the end of the period. The annual rate is divided by the number of periods a year to get the periodic one, which is the nominal convention banks quote.
Compounding more often on the same nominal rate earns more, because interest starts earning sooner. The effective annual rate shown is what that comes to over a year: 12% compounded monthly is 12.68% effective.
Examples
| Case | Input | Result |
|---|---|---|
| Saving monthly for ten years | 1,000 start, 100 a month, 5%, 10 years | 17,175.24, of which 4,175.24 is interest |
| A lump sum left alone | 10,000 start, nothing added, 7%, 20 years | 38,696.84 |
Frequently asked questions
What rate should I use?
Yours. This tool has no default return, no historical average and no assumption about markets, because those are claims about the world that a formula has no business making. Use the rate your account pays, or try a range and see how much the answer moves.
Is inflation taken into account?
No. The result is a nominal amount, not adjusted for prices. A balance that grows at 5% while prices rise at 3% has gained about 2% in purchasing power, and this figure does not show that.
Are contributions added at the start or the end of the period?
At the end, which is the ordinary annuity convention and the conservative one. Paying at the start of each period earns one extra period of interest on every contribution and gives a slightly higher figure.
Good to know
- Amounts carry no currency: the answer is in whatever you put in.
- Results use double precision floating point arithmetic. That is exact enough to decide with and is not an accounting record.
- Nothing here is a projection or a forecast: it is arithmetic on the rate you supplied, applied unchanged for the whole term.