Finance & Money
Rates & guidance reviewed
Compound interest is interest earned on both your original money and the interest already added. Over years, regular contributions plus compounding can grow a savings or investment pot far more than a single lump sum alone.
This free calculator projects a future balance from a starting amount, optional monthly contributions, an annual rate, term and compounding frequency (monthly, quarterly, annually or daily). Results update in your browser — nothing is uploaded.
Figures are illustrative. Real products have fees, tax, variable rates and market risk. Use the tool to compare “what if” scenarios, not as a guaranteed forecast.
Compound interest formula · illustrative growth only
Can be 0 for lump sum only
Illustrative only. Does not model ISA/pension tax wrappers, inflation, variable rates, fees or sequence of returns risk.
Static sample calculations you can read without using the form. Figures match this tool's maths — always re-run with your own numbers for a personal estimate.
The default: lump plus a standing order, compounded monthly.
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Same figures as the written compound-interest guide. Annual compounding on the same cashflows is £38,331.42.
No monthly contribution — interest on the lump only.
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Save from zero. Time and rate do more work than a small lump.
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Only compounding frequency changes.
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Monthly versus annual is £960.08. Daily versus monthly is £87.74.
If you invest £1,000 at 5% compounded annually, you have £1,050 after one year. In year two, interest is calculated on £1,050, not just the original £1,000. Over decades, that snowball effect is powerful — especially when you keep adding contributions.
Compounding more frequently (for example monthly vs annually) slightly increases the effective annual yield for the same nominal rate. Monthly contributions are modelled as regular additions spread across the year according to the compounding schedule.
Inflation reduces purchasing power over time. A balance that grows at 4% while inflation is 3% only gains about 1% in real terms before tax and fees. ISAs and pensions can change the tax outcome — this tool ignores tax wrappers.
Future value is the lump compounded, plus an ordinary annuity of the contributions, at the rate per compounding period. On the default, the £5,000 lump alone is £8,235.05, the £200-a-month stream is £31,056.46, and together £39,291.50. A longer walk-through of that split, compounding frequency, a save-from-zero example, and why inflation is a different calculator is in the written compound-interest guide.
Always confirm rates, bands and eligibility on official pages. Our tools are simplified estimators for guidance only.