Financial calculator
See how your money could grow.
Project savings or investment growth with regular contributions and a fixed interest-rate assumption.
Calculate compound interest
Illustrative onlyRegular contribution
Projected final balance
£47,526.55
After 10 years at a fixed 5% nominal annual rate with monthly compounding
- Starting amount£10,000.00
- Regular contributions£24,000.00
- Interest earned£13,526.55
How was this calculated?
The compound-interest formula A = P(1 + r/n)^(nt) describes the lump-sum part of this projection. Your 5% nominal annual rate is converted using monthly compounding, producing an effective annual rate of 5.12% and an equivalent growth factor for each calculation period.
This projection covers 10 years. It uses monthly contributions, added at the end of each selected period. No annual contribution increase is applied.
Total contributed £34,000.00 plus interest earned £13,526.55 gives the projected final balance of £47,526.55. Interest is calculated without rounding until the final display.
Projection
Your balance over time
| Period | Contributions | Interest | End balance |
|---|---|---|---|
| Year 1 | £2,400.00 | £567.39 | £12,967.39 |
| Year 2 | £4,800.00 | £1,286.60 | £16,086.60 |
| Year 3 | £7,200.00 | £2,165.39 | £19,365.39 |
| Year 4 | £9,600.00 | £3,211.93 | £22,811.93 |
| Year 5 | £12,000.00 | £4,434.80 | £26,434.80 |
| Year 6 | £14,400.00 | £5,843.03 | £30,243.03 |
| Year 7 | £16,800.00 | £7,446.09 | £34,246.09 |
| Year 8 | £19,200.00 | £9,253.96 | £38,453.96 |
| Year 9 | £21,600.00 | £11,277.11 | £42,877.11 |
| Year 10 | £24,000.00 | £13,526.55 | £47,526.55 |
How it works
Interest can earn further interest over time
Compound interest means growth is added to the balance, so later interest is calculated on the starting amount and earlier growth. This differs from simple interest, which is calculated only on the original amount.
Enter a starting balance, nominal annual rate and term. You can then model regular weekly, fortnightly, monthly, quarterly, half-yearly or annual contributions, choose whether they are made at the beginning or end of the period, and optionally increase them each year.
The compounding frequency matters because it determines how often the nominal rate is applied. The calculator converts the selected convention into an effective annual rate and an equivalent monthly growth factor for its projection.
Understanding your result
Separate what you pay in from the growth assumption
The projected final balance combines your starting amount, regular contributions and estimated interest. “Total contributed” is money you have added; “interest earned” is the modelled growth above those contributions. The yearly table shows how that balance could build over the selected term.
Contribution timing changes the result. A contribution made at the beginning of a period has that period in which to earn interest, while an end-of-period contribution does not. Increasing contributions can also have a large cumulative effect over a long term.
Worked example
For example, £10,000 growing for 10 years at a fixed 5% nominal annual rate, compounded monthly, with £200 added at the end of each month would produce a projected balance of about £47,527. Of that, £34,000 is the starting amount plus contributions and about £13,527 is modelled interest.
This example assumes the same rate throughout, no withdrawals and no fees, tax or inflation. It illustrates the calculation rather than predicting an available savings rate or investment return.
Assumptions and limitations
A smooth projection is not a forecast
The calculator applies one fixed non-negative rate for the whole term. Savings rates can change, and investment values can rise or fall rather than grow smoothly. A higher assumed return can make a very large difference over longer periods, but it does not make that return more likely.
The result does not deduct product charges, platform or advice fees, tax, withdrawals or the effect of inflation. It also does not assess whether a savings account or investment is suitable for you. For a more realistic comparison, use a cautious range of rates and consider each of those costs separately.
Independent information
Check rates, risk and purchasing power
MoneyHelper explains how savings interest rates and compounding work. If you are modelling investments, read the Financial Conduct Authority’s information about risk and returns. The Bank of England also explains how inflation affects purchasing power.
Related calculators
Measure an investment’s annualised historical growth with the CAGR Calculator, model contributions and withdrawals with the Investment Calculator, or estimate when you could reach a target with the How Long to Save Calculator.