Compound Interest Calculator
See what regular contributions and compounding actually produce, year by year, split into what came from your initial deposit, your contributions, and interest.
- Final balance
- $300,850.72
- Contributed
- $130,000.00
- Interest
- $170,850.72
- Effective rate
- 7.229%
Money in
The starting lump and the recurring deposit
The contribution is added once per compounding period, at the end of that period. With daily compounding that is 365 deposits a year, not 12 — change the frequency if you only intend a monthly deposit.
Terms
Rate, horizon and how often interest is added
12 compounding periods a year — the usual default.
- Periods simulated
- 240
- Rate per period
- 0.58333%
- Doubles in
- 9.93 years
Growth by year
Each bar is the whole balance at that year, split into where it came from
Peak shown $300,850.72 — year 20.
Final balance
After 240 compounding periods
$300,850.72
You put in
Initial principal plus every contribution
$130,000.00
43.2% of the final balance
Interest earned
The compounding working for you
$170,850.72
131.4% return on money you paid in
Where the final balance came from
Principal and interest growth are attributed proportionally as interest accrues
- Initial principal, grown$40,387.39
- Contributions, grown$260,463.33
- Interest on top$0.00
Rate check
Nominal against the rate you actually earn
- Nominal annual rate
- 7.000%
- Effective annual rate (EAR)
- 7.229%
- Compounding gain from frequency
- +0.229 pts
- Doubling time (exact)
- 9.93 years
- Doubling time (rule of 70)
- 10.00 years
EAR is (1 + r/n)ⁿ − 1. It is the number that belongs in an APR comparison, and the one your bank must quote. The rule of 70 is a rough shortcut; the exact figure above uses ln 2 / ln(1 + EAR).
Year-by-year
Sampled from the same simulation that drew the chart
| Year | Balance | From initial | From contributions | Interest | Paid in so far |
|---|---|---|---|---|---|
| 1 | 16.9k | 10.7k | 6.2k | 0 | 16.0k |
| 2 | 24.3k | 11.5k | 12.8k | 0 | 22.0k |
| 3 | 32.3k | 12.3k | 20.0k | 0 | 28.0k |
| 4 | 40.8k | 13.2k | 27.6k | 0 | 34.0k |
| 5 | 50.0k | 14.2k | 35.8k | 0 | 40.0k |
| 6 | 59.8k | 15.2k | 44.6k | 0 | 46.0k |
| 7 | 70.3k | 16.3k | 54.0k | 0 | 52.0k |
| 8 | 81.6k | 17.5k | 64.1k | 0 | 58.0k |
| 9 | 93.7k | 18.7k | 74.9k | 0 | 64.0k |
| 10 | 106.6k | 20.1k | 86.5k | 0 | 70.0k |
| 11 | 120.5k | 21.5k | 99.0k | 0 | 76.0k |
| 12 | 135.5k | 23.1k | 112.3k | 0 | 82.0k |
| 13 | 151.4k | 24.8k | 126.7k | 0 | 88.0k |
| 14 | 168.6k | 26.6k | 142.0k | 0 | 94.0k |
| 15 | 187.0k | 28.5k | 158.5k | 0 | 100.0k |
| 16 | 206.7k | 30.5k | 176.1k | 0 | 106.0k |
| 17 | 227.8k | 32.8k | 195.1k | 0 | 112.0k |
| 18 | 250.5k | 35.1k | 215.4k | 0 | 118.0k |
| 19 | 274.8k | 37.7k | 237.1k | 0 | 124.0k |
| 20 | 300.9k | 40.4k | 260.5k | 0 | 130.0k |
Assumes a constant rate and constant contributions, no fees, no tax, and no inflation. Real returns vary year to year, and this is a projection, not advice.