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Compound Interest Calculator

See how compound interest grows your savings over time with regular deposits.

Inputs

Final Balance
$50,969.84
Monthly compounded • 10 yrs
Total Principal
$34,000.00
Total Interest
$16,969.84

Account value over time

Projected growth of your $34,000.00 in contributions to $50,969.84 over 10 years — earning $16,969.84 in interest. Projected value, not guaranteed.

$51k$25k$0Yr 0Yr 2Yr 4Yr 6Yr 8Yr 10Value ($)

What is the Compound Interest Calculator?

A compound interest calculator is a free online tool that shows how your savings or investment grows when interest is added to the principal and itself earns interest. Use it to see the long-term effect of compounding frequency, regular deposits, and a higher contribution rate.

Compound Interest Calculator formula

Compound interest uses A = P × (1 + r/n)^(n × t), where P is principal, r is the annual rate, n is compounding periods per year, and t is years. With monthly deposits PMT, add PMT × [((1 + r/n)^(n × t) − 1) / (r/n)]. Total interest earned = A − P − (PMT × n × t).

How to use the Compound Interest calculator

  1. 1Enter the initial deposit (principal).
  2. 2Enter the annual interest rate.
  3. 3Choose the compounding frequency (daily, monthly, quarterly, or annually).
  4. 4Enter any regular monthly contributions you plan to add.
  5. 5Enter the time horizon in years, then review the final balance, total contributions, and interest earned.

Example calculation

$5,000 invested at 7% compounded monthly, with $250 added each month for 20 years, grows to about $150,428. That breaks down to $65,000 in total contributions ($5,000 initial + $60,000 monthly) and $85,428 in compound interest.

Frequently asked questions

How is compound interest calculated?
Use A = P × (1 + r/n)^(n × t), where P is principal, r is the annual rate, n is compounding periods per year, and t is years. For monthly compounding, set n = 12. The total interest earned is A minus the principal.
How much will $10,000 be worth in 20 years at 5% compound interest?
$10,000 invested at 5% compounded monthly for 20 years grows to $27,126.40 — earning $17,126.40 in interest. Compounded annually, it grows to $26,532.98, showing how compounding frequency matters.
What is the difference between simple and compound interest?
Simple interest is earned only on the original principal. Compound interest is earned on the principal plus any previously earned interest. Over long periods, compounding produces dramatically more growth than simple interest.
What is the Rule of 72?
The Rule of 72 estimates how long it takes money to double: divide 72 by the annual interest rate. At 8% annual return, money doubles in about 9 years (72 ÷ 8). At 6%, it takes 12 years.

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