Finance & Money
Compound Interest / Savings Calculator
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.
Interactive tool
Compound interest formula · illustrative growth only
Can be 0 for lump sum only
Projected balance
Illustrative only. Does not model ISA/pension tax wrappers, inflation, variable rates, fees or sequence of returns risk.
How to use this tool
- Enter your starting balance (use 0 if you only contribute monthly).
- Add any regular monthly contribution.
- Set the expected annual interest or growth rate and the number of years.
- Choose how often interest compounds.
- Review future value, total contributed and interest earned; copy results to compare plans.
Why compounding matters
If you invest £1,000 at 5% compounded annually, you have about £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.