Savings & Compound Interest Calculator
See how your savings grow over time with compound interest and regular contributions.
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projected balance
| Total you put in | – |
|---|---|
| Interest earned | – |
Compound interest savings calculator
This calculator shows how your savings can grow over time thanks to compound interest. Enter a starting amount, an optional monthly contribution, the interest rate, and how many years you will save for. It projects your final balance and splits it into the money you contributed and the interest you earned.
The power of compounding
Compound interest means you earn interest not only on your original savings but also on the interest already added. Over many years this snowball effect becomes powerful — which is why starting early and contributing regularly matters far more than the exact rate. The calculator compounds monthly and adds your contribution each month for a realistic projection.
Using it for goals
Use it to plan for a house deposit, an emergency fund, or any savings goal. For longer-term retirement planning, our investment & retirement calculator projects a pension pot, and the budget calculator helps you find money to save each month.
Frequently asked questions
Does it account for tax or inflation?
No. It shows growth before tax and in today's money. Tax-free accounts (like an ISA) and inflation will both affect your real result. Read our guide: how much £100 a month becomes with compound interest.
Disclaimer: This calculator provides estimates for informational purposes only and is not financial advice. Investment returns are not guaranteed and the value of investments can fall as well as rise.
The compound interest formula with monthly saving
The calculator combines two parts: the growth of your starting amount and the growth of each monthly contribution. With monthly compounding, the future value is FV = P × (1 + r)n + C × [((1 + r)n − 1) ÷ r]. Here P is the starting amount, C is the monthly contribution, r is the annual rate divided by 12, and n is the number of months.
Worked example
Suppose you start with £5,000, add £200 a month, and earn 5% a year compounded monthly for 10 years. The monthly rate is 0.05 ÷ 12 = 0.004167 and n is 120. The starting £5,000 grows to about £8,235, and the monthly contributions grow to about £31,056. The total is roughly £39,291, of which £29,000 is money you paid in and around £10,291 is interest.
What £200 a month can grow to
| Annual rate | 10 years | 20 years | 30 years |
|---|---|---|---|
| 3% | £27,948 | £65,660 | £116,547 |
| 5% | £31,056 | £82,207 | £166,452 |
| 7% | £34,617 | £104,185 | £243,994 |
Total contributions are £24,000 after 10 years, £48,000 after 20 and £72,000 after 30. The table shows how time does most of the work: at 7%, interest makes up more than two-thirds of the 30-year total. The same figures apply in dollars or euros because the currency does not change the maths. For a smaller monthly amount, see what £100 a month becomes with compound interest.
The rule of 72
For a quick mental check, divide 72 by the annual interest rate to estimate how many years it takes a lump sum to double. At 5% that is about 14.4 years, and at 8% about 9 years. It is an approximation, but it is accurate to within a few months for rates between 4% and 10%.
Things the calculator does not include
The results show growth before tax, fees and inflation. Bank accounts usually quote an AER or APY, which already includes the effect of compounding, so enter that figure as the annual rate. Interest on savings may be taxable above your personal allowance, although UK ISAs and some US retirement accounts shelter growth from tax. Inflation reduces what your future balance can buy: at 2.5% inflation, £39,291 in ten years has the buying power of roughly £30,700 today. Investment returns are not guaranteed and can go down as well as up. This tool is for illustration only and is not financial advice.