What is compound interest?

It is interest earned on both the original balance and past interest.

Can I add monthly deposits here?

Use the savings calculator for regular monthly contributions.

CalcBeacon tool

Compound Interest Calculator

Estimate how savings or investments grow with principal, contributions, interest rate, time and compounding.

Start calculator View category

Calculator

Use the compound interest calculator

Calculate compound growth from a starting balance, rate and years.

Principal

Annual rate (%)

Years

Compounds per year

Result: waiting for input

Enter your values to see the result.

Visual projection

Use the chart to see how the balance grows over time.

Quick Guide

Quick answer

Compound Interest Calculator: Compound interest means interest is calculated on both the original amount and previously earned interest. Time, rate, contributions and compounding frequency all affect the final balance.

Formula / core ruleFuture value = principal × (1 + rate ÷ n)^(n × years), before adjusting for regular contributions.

This is the main calculation rule used by the tool.

Worked example£1,000 invested for 10 years at 5% compounded annually grows to about £1,628.89 before fees, taxes or extra contributions.

Use the example to check whether your own inputs are in the right range.

Common mistakeDo not treat the annual interest rate as guaranteed investment return. Real returns can vary, and fees, tax and inflation reduce purchasing power.

This is the most common reason the result can look wrong.

How to interpret the result

The result shows estimated future value, growth and contribution impact under the assumptions entered. Longer time horizons make compounding more powerful.

Methodology

The calculator applies the compound interest formula using your principal, rate, time and compounding frequency. Where contributions are included, it adds them according to the chosen schedule.

Important decisions should be checked against payslips, lender documents, tax guidance, official policy or professional advice where relevant.

Reviewed by CalcBeacon Editorial TeamUpdated June 2026Category: Finance CalculatorsFormula, example and assumptions shown

Practical Guide

How to use this result well

Use this compound interest calculator to see how money can grow when interest is added to the balance and starts earning interest itself.

What the result means

The result shows estimated future value, growth and contribution impact under the assumptions entered. Longer time horizons make compounding more powerful.

Common mistakes to avoid

Entering 5 instead of 0.05 in tools that expect decimal rates, or the reverse
Ignoring fees, taxes and inflation
Assuming a fixed return for investments that can rise and fall

When to double-check

Double-check the result when money, employment rights, borrowing, tax, health or official paperwork depends on the number. CalcBeacon is designed to make the maths clearer, not to replace professional judgement.

Frequently asked questions

What makes compound interest powerful?

Interest begins earning interest, so growth can accelerate over longer periods.

Does compounding frequency matter?

Yes. More frequent compounding can slightly increase the final balance when the same annual rate is used.

Is the result guaranteed?

No. It is a projection based on your inputs, not a guaranteed return.

How it works

Formula

A = P(1 + r/n)^(nt)

Example

£5,000 at 5% for 10 years compounded monthly will end higher than the same money with simple interest.