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Interest Calculator - Simple and Compound Interest

Calculate simple or compound interest in one tool

Switch between simple and compound interest to find the interest earned and the total amount from a principal, rate, and time — free and instant.

Principal ($)
Annual rate (%)
Time (years)

Interest

Enter all values

Total amount

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About the interest calculator - simple and compound interest

The Interest Calculator combines simple and compound interest into a single tool. Choose Simple to compute interest charged only on the original principal, or choose Compound to see how an investment or loan grows when interest is reinvested and itself earns interest. Enter the principal, annual rate, and time in years; for compound interest, also set how many times per year the interest compounds.

Simple interest suits short-term loans, bonds, and basic savings where interest is not reinvested. Compound interest is the engine behind long-term investing and most loans — the more frequently interest compounds, the faster the balance grows. Common frequencies are yearly (1), quarterly (4), monthly (12), and daily (365).

The formulas behind the result

  • Simple Interest = (Principal × Rate × Time) ÷ 100
  • Simple Total = Principal + Simple Interest
  • Compound Amount = Principal × (1 + Rate ÷ (100 × n))^(n × Time)
  • Compound Interest = Compound Amount − Principal
  • n = number of times interest compounds per year (compound mode only).

How to use the interest calculator - simple and compound interest

  1. Pick simple or compound

    Use the toggle to choose the interest type you want to calculate.

  2. Enter the principal, rate, and time

    Type the amount, the yearly rate as a percentage, and the duration in years.

  3. Set compounding frequency (compound only)

    Enter how many times per year interest compounds (12 = monthly). The interest and total appear instantly.

Frequently asked questions

What is the difference between simple and compound interest?
Simple interest is charged only on the original principal and grows linearly. Compound interest is charged on the principal plus accumulated interest, so it grows at an accelerating rate over time.
When should I use simple interest?
Use it for short-term loans, bonds, and basic savings accounts where interest is not reinvested into the principal.
When should I use compound interest?
Use it for long-term investments, savings with reinvested interest, and most loans where interest is added back to the balance.
What compounding frequency should I use?
Savings accounts often compound monthly (12) or daily (365). Loans may compound monthly. Pick the frequency that matches your product.
What units should I use for time?
Enter time in years. For 6 months, enter 0.5; for 18 months, enter 1.5.
Is the interest calculator free?
Yes, it is completely free and requires no sign-up.

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