Free compound interest calculator

Project how savings and returns could grow over time.

Estimate how an initial deposit, regular monthly contributions, and a steady annual return could affect your future balance.

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Monthly compounding

Contributions are added at the end of each month after growth is applied.

Projected final balance

£129,885

Includes £59,885 of estimated growth over 20 years.

Inputs

Savings details

CurrencyFor display onlyInitial depositStarting balanceMonthly contributionAdded each monthAnnual returnEstimated %Time horizonYears

Estimate

Results

Projected final balance

£129,885

Total contributions

£70,000

Estimated growth

£59,885

Assumes a steady annual return compounded monthly. Actual returns may vary and investments can fall as well as rise.

Projection

Investment balance over time

ContributionsProjected balance

Important disclaimer

This calculator provides estimates only and does not constitute financial advice, investment advice, or a guarantee of returns. Actual performance may vary due to fees, taxes, market conditions, inflation, and provider terms.

Review the OverPayWise methodology and editorial standards

Understand the lesson behind Compound Interest Calculator.

Use the education page before relying on the result. It explains the assumptions, shows the maths, gives worked examples, and includes practice questions so the estimate is easier to check.

Tutorial

Use the investing part of the overpay-vs-invest lesson to understand compound return assumptions.

Maths lesson

Covers monthly contributions, assumed returns, compounding, uncertainty, fees, and tax drag.

Worked examples

Works through spare cash growing monthly and compares the estimate with mortgage interest saved.

Practice questions

Practise changing the assumed return and explaining why the result is not a guarantee.