Compound interest
Compound interest calculator with contributions
Project how a starting amount plus regular deposits grows over time. Choose monthly or annual compounding, add an inflation adjustment, and see a clear chart and year-by-year breakdown.
Run your projection
Contributions are added at the end of each period (ordinary annuity).
Future value
£144,573
Total contributions
£58,000
Investment growth
£86,573
Balance over time
Stacked: your contributions vs. compounded growth.
Year-by-year breakdown
| Year | Balance | Contributions | Growth |
|---|---|---|---|
| 1 | £13,201 | £12,400 | £801.42 |
| 2 | £16,634 | £14,800 | £1,834 |
| 3 | £20,315 | £17,200 | £3,115 |
| 4 | £24,262 | £19,600 | £4,662 |
| 5 | £28,495 | £22,000 | £6,495 |
| 6 | £33,033 | £24,400 | £8,633 |
| 7 | £37,900 | £26,800 | £11,100 |
| 8 | £43,118 | £29,200 | £13,918 |
| 9 | £48,714 | £31,600 | £17,114 |
| 10 | £54,714 | £34,000 | £20,714 |
| 11 | £61,147 | £36,400 | £24,747 |
| 12 | £68,046 | £38,800 | £29,246 |
| 13 | £75,444 | £41,200 | £34,244 |
| 14 | £83,376 | £43,600 | £39,776 |
| 15 | £91,882 | £46,000 | £45,882 |
| 16 | £101,003 | £48,400 | £52,603 |
| 17 | £110,783 | £50,800 | £59,983 |
| 18 | £121,270 | £53,200 | £68,070 |
| 19 | £132,515 | £55,600 | £76,915 |
| 20 | £144,573 | £58,000 | £86,573 |
What this calculator tells you
Compound interest is the single most powerful force in long-term investing. This calculator separates the money you contribute from the growth those contributions generate, so you can see exactly how much of your future balance is compounding rather than saving.
Use the advanced options to add an annual contribution increase (handy if you plan to invest more as your income rises) and an inflation rate to keep the result grounded in today's money.
How compounding works
Compounding is growth on growth. Each period, your returns are added to your balance — and the next period earns returns on that larger balance too. Over long horizons this snowball effect dwarfs your original contributions.
A lump sum grows by FV = PV × (1 + r)ⁿ, where r is the periodic rate and n the number of periods. Monthly compounding splits the annual rate into twelve.
Regular deposits form an annuity:FV = PMT × [(1 + r)ⁿ − 1] / r. We add contributions at the end of each period (ordinary annuity).
With DRIP, dividends buy more shares, which pay more dividends. Add dividend growth and your yield on cost rises year after year — the engine behind real passive income.
Why time matters more than rate
Invest £10,000 at 7% with no further deposits and you have roughly £19,672 after 10 years, but about £76,123 after 30 years. The extra two decades did far more than the first one — because each year compounds on an ever-larger base. Starting earlier usually beats trying to earn a higher return.
Pick the right calculator
One engine, four lenses. Each mode tailors the inputs and outputs for a specific question — all using the same correct compounding math.
Ready to put compounding to work?
A projection only matters once you start investing. These are starting points to research a broker or ETF platform that suits you. We are not recommending a specific product — compare fees, eligibility and protections before you commit.
Affiliate disclosure: some links may be sponsored and we may earn a commission at no cost to you. This is not financial advice.
Frequently asked questions
How is compound interest calculated with regular contributions?
The lump sum grows by FV = PV × (1 + r)ⁿ. Each contribution is treated as part of an ordinary annuity and grows by FV = PMT × [(1 + r)ⁿ − 1] / r, where r is the periodic rate and n the number of periods. Compoundly combines both and shows the total, plus the split between contributions and growth.
What is the difference between monthly and annual compounding?
With monthly compounding the annual rate is divided by twelve and applied each month, so interest is earned on interest more often, producing a slightly higher result than annual compounding at the same nominal rate.
Can I see the inflation-adjusted (real) value?
Yes. Open the advanced section and enter an inflation rate. Compoundly then shows the real, purchasing-power value of your ending balance alongside the nominal figure.
What return rate should I use?
There is no guaranteed rate. Historically a globally diversified equity index has returned around 7% per year after inflation over long periods, but returns vary widely and the future may differ. Try a range of rates to understand the spread of outcomes.