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Compound Interest Calculator
The single most important concept in personal finance, made visible. Plug in an initial deposit, a monthly contribution, an expected annual return, and a time horizon — see what compounding actually does. Includes a year-by-year breakdown so you can see exactly where the growth comes from (and how much of it is interest vs contributions).
What it does
- Initial deposit + monthly contributions
- Custom annual return rate
- Year-by-year breakdown table
- Total contributions vs total growth split
- Inflation-adjusted (real) view toggle
Starting point
Growth assumptions
The headline
Final balance · year 25
£209,425
Nominal terms
Total contributions
£76,000
36.3% of the final pot
Interest / growth
£133,425
63.7% of the final pot
What's in the final pot
36%
64%
Your contributions Growth from compounding
Year 18 is when compound growth overtakes your own contributions — the point where the money starts doing the heavy lifting for you.
Year by year
| Year | Contributed | Growth | Balance |
|---|---|---|---|
| 1 | £3,000 | £189 | £4,189 |
| 2 | £3,000 | £419 | £7,608 |
| 3 | £3,000 | £666 | £11,274 |
| 4 | £3,000 | £931 | £15,205 |
| 5 | £3,000 | £1,215 | £19,420 |
| 6 | £3,000 | £1,520 | £23,940 |
| 7 | £3,000 | £1,847 | £28,787 |
| 8 | £3,000 | £2,197 | £33,984 |
| 9 | £3,000 | £2,573 | £39,557 |
| 10 | £3,000 | £2,976 | £45,533 |
| 11 | £3,000 | £3,408 | £51,941 |
| 12 | £3,000 | £3,871 | £58,812 |
| 13 | £3,000 | £4,368 | £66,180 |
| 14 | £3,000 | £4,900 | £74,080 |
| 15 | £3,000 | £5,471 | £82,552 |
| 16 | £3,000 | £6,084 | £91,636 |
| 17 | £3,000 | £6,741 | £101,376 |
| 18crossover | £3,000 | £7,445 | £111,821 |
| 19 | £3,000 | £8,200 | £123,021 |
| 20 | £3,000 | £9,009 | £135,030 |
| 21 | £3,000 | £9,878 | £147,908 |
| 22 | £3,000 | £10,808 | £161,716 |
| 23 | £3,000 | £11,807 | £176,523 |
| 24 | £3,000 | £12,877 | £192,400 |
| 25 | £3,000 | £14,025 | £209,425 |
Compounded monthly. Returns are assumed constant for clarity — real markets are lumpy. This is a planning tool, not a forecast. Past performance never guarantees future returns.