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Interest Calculator: Compound Interest & Savings

The first time I ran the compound interest numbers properly, I understood why starting early matters so much more than the interest rate itself. This calculator shows the difference with your own numbers.

Interest Calculator – Compound Interest & Savings

Calculate interest for savings accounts, fixed deposits and savings plans: with compound interest

£
%
Years
£
Final Amount
£14,105.99
after 10 years at 3.5% compound interest
Contributions
£10,000.00
Interest Earned
£4,105.99
Breakdown
Contributions£10,000.00
Interest Earned£4,105.99
Total Return41,1 %

What does the Interest Calculator calculate?

Simple Interest Interest is only calculated on the original capital – without compounding of returns.
Compound Interest Interest is calculated on the capital and on previously earned interest. Over time this creates exponential growth.
Annual Deposit Regular annual contributions in addition to the starting capital – for savings plans or easy-access accounts.

The compound interest effect is one of the most powerful mechanisms in saving and investing. The longer the investment period, the stronger it works. Even small differences in interest rate lead to enormous differences in final capital over 20–30 years.

Tip: Compare simple interest and compound interest with the same amount – and see how large the difference is after 20 years.

Frequently Asked Questions

With simple interest, returns are calculated only on the original capital. With compound interest, earned interest is added to the capital and earns interest itself. Over long periods the difference is enormous.
With compound interest at 3.5% over 10 years, €10,000 grows to €14,106. Interest earned: €4,106. With simple interest it would only reach €13,500.
For a classic savings account or fixed deposit, 2–4% p.a. is realistic in 2026. For a broad ETF like the MSCI World, the historical average has been 7–8% p.a.: but with more volatility.
Divide 72 by the annual interest rate to get the approximate number of years it takes to double your money. At 4%: 18 years. At 8%: 9 years.

Related Guides

Compound Interest GuideHow it really worksETF Savings PlanCompound interest with monthly contributionsEasy Access vs Fixed RateWhere to get more interestLoan CalculatorMonthly payment & repayment schedule

⚠️ All calculations are for guidance only. Not a substitute for professional financial advice.