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Compound Interest Calculator

See how your money grows with compound interest over time. Enter your principal, interest rate, compounding frequency, and time period to see the power of compounding in action.

Part of our Finance Calculators collection.

Compound Interest Calculator

Free online calculator

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Regular deposits added each month

How to Use This Calculator

  1. 1

    Enter your starting amount (principal).

  2. 2

    Enter the annual interest rate your investment earns.

  3. 3

    Select how often interest compounds — monthly is common for savings accounts; annually for many investments.

  4. 4

    Set the time period in years.

  5. 5

    Optionally add a monthly contribution to see how regular saving accelerates growth.

Compound Interest Formula

A = P × (1 + r/n)^(n×t)

A = final amount, P = principal, r = annual rate, n = compounding periods per year, t = years

With regular contributions:
A = P × (1 + r/n)^(nt) + PMT × [((1 + r/n)^(nt) − 1) / (r/n)]

Example Calculation

Example: $10,000 at 8%, monthly compounding, 10 years

Inputs

principal: 10000annualRate: 8compoundFrequency: 12years: 10monthlyContribution: 200

Result

$58,722 final balance

$10,000 principal plus $200/month at 8% compounded monthly grows to $58,722 in 10 years. You contributed $34,000 — compound interest added $24,722.

Frequently Asked Questions

What's the difference between compound and simple interest?
Simple interest is calculated only on the principal. Compound interest is calculated on the principal plus all previously earned interest. Over time, the difference becomes dramatic — this is what Einstein reportedly called the 'eighth wonder of the world.'
How often should interest compound?
The more frequently interest compounds, the faster your money grows. Daily compounding earns slightly more than monthly, which earns more than annual — but the differences are small compared to getting your rate right.
What's the Rule of 72?
Divide 72 by your annual interest rate to estimate how many years it takes to double your money. At 8%, your money doubles in about 9 years (72 ÷ 8 = 9).

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