Compound Interest Calculator

This compound interest calculator helps you estimate how your investment grows over time. Compound interest is a method where the interest earned is added back to the principal sum, so that interest in the next period is earned on the principal plus previously accumulated interest. Simply put: interest starts earning interest.

This is how bank deposits with capitalization, loans, and most investment instruments work.

You can also add regular monthly contributions or withdrawals to see how they affect the final balance alongside compound interest.

Calculator

monetary units
monetary units
% per year
number of years

Withdrawals

The calculator supports monthly withdrawals. To do this, enter the withdrawal amount with a minus sign (e.g., -500). In the results, the total amount of withdrawals will be shown in the 'Total additions' field with a minus sign.

Compound Interest Formula

S = P × (1 + r/n)^(n×t)

  • S — the future value of the investment
  • P — the principal investment amount
  • r — the annual interest rate (decimal, e.g., 0.15 for 15%)
  • n — the number of times that interest is compounded per year (monthly = 12, quarterly = 4, annually = 1)
  • t — the number of years

Example: $100,000 at 15% interest for 3 years with monthly compounding:
S = 100,000 × (1 + 0.15/12)^(12×3) = $156,394
Growth — $56,394 without any additional contributions.

Compound vs Simple Interest

With simple interest, the principal remains constant — interest is always calculated based on the original amount. With compound interest, the interest is added to the principal, and the next interest calculation is based on the new, higher balance.

For example, $100,000 at 15% for 3 years yields $145,000 with simple interest — but $156,394 with monthly compounding. The longer the term, the greater the effect of compounding and the wider the gap between the two methods.

Use Specialized Calculators

This calculator shows the general mathematics of compound interest. For precise calculation of a specific financial product, use: