Compound Interest Calculator
Future value with an annual rate, compounding frequency and optional monthly additions. Figures update as you type.
Growth over time
How to use the Compound Interest Calculator
- Enter your Initial Investment in pounds (£).
- Add a Monthly Contribution if you plan to pay in regularly (use 0 if not).
- Set the Annual Interest Rate as a percentage.
- Choose the Investment Period in years.
- Select Compounding Frequency: Annually, Semi-annually, Quarterly, Monthly or Daily.
- Read the breakdown: initial investment, monthly contributions total, interest earned and total value.
If you enjoy what we do, consider supporting us. Every little bit means the world! Support Catpool on Ko-fi
What it is for
Compound interest means you earn interest on both the original sum and on interest already added. Over several years, that snowball effect can make a large difference compared with simple interest. This calculator estimates how a lump sum, optional monthly top-ups and a stated annual rate could grow when interest is compounded at the frequency you choose.
Worked example: suppose you start with £5,000, contribute £150 each month, earn 4% a year and leave the money for 10 years with monthly compounding. The tool shows how much of the final figure came from your own deposits and how much from interest. Change the rate or the period and you can compare “what if” scenarios side by side without a spreadsheet.
That is handy for rough savings goals, comparing contribution habits, or sense-checking a figure you have been quoted. It is an estimate only, not financial advice, and not a forecast of any particular product. Real accounts may charge fees, vary rates, or compound on different schedules. For other everyday figures, try the Percentage Calculator or the Mortgage Calculator.
Why it runs in your browser
Your amounts stay on the page. Nothing is uploaded, and there is no sign-up. That keeps private savings figures off someone else’s server while you explore different scenarios.
Common questions
What does compounding frequency mean?
It is how often interest is added to the balance. Daily and monthly compounding generally grow a little faster than annual compounding at the same nominal rate, because interest starts earning interest sooner. Pick the option that best matches the product you are comparing.
Should I include monthly contributions?
If you pay in regularly, yes. Even modest monthly amounts add up over a decade. If you only have a one-off lump sum, set Monthly Contribution to 0 so the result reflects growth on the initial investment alone.
Is the result guaranteed?
No. The calculator applies the rate and schedule you enter. Markets, providers and tax treatment can change. Treat the total as an illustration for planning conversations, not a promise.
Can I use it for debts as well as savings?
The same maths describes growth on a balance. For borrowing, interpret carefully: rates, fees and repayment rules differ. This page is framed around savings and investments; for loan-style payments see tools such as the mortgage calculator where relevant.
Why show initial investment, contributions and interest separately?
So you can see how much of the final total is money you put in versus interest earned. That split makes it clearer whether a goal is driven more by deposits or by the rate.
Related: Calculators, Percentage Calculator, VAT Calculator.
