Interest Calculator

Calculate simple or compound interest and see how your money grows over time. Get instant results with charts and year-by-year breakdown.

Your Details

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Enter your principal, interest rate, and time period. Choose simple or compound interest, then click Calculate to see your results with charts and yearly breakdown.

Complete User Guide

What is Simple vs Compound Interest?

Simple interest is calculated only on the principal. Compound interest is calculated on the principal plus accumulated interest. Compound interest grows faster because you earn "interest on interest."

Simple: I = P × r × t

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

What Your Results Mean

Final Amount

The total value at the end of the period: principal plus interest earned.

Interest Earned

The total interest over the period. For compound interest, this includes interest on interest.

Effective Rate

For simple interest, this equals the stated rate. For compound interest, it reflects the actual annual return after compounding.

How to Use This Calculator

  1. Enter your principal (starting) amount
  2. Enter the annual interest rate and time period (years, months, or days)
  3. Choose simple or compound interest
  4. For compound interest, select compounding frequency (monthly, daily, etc.)
  5. Click Calculate to see results, comparison, and yearly breakdown

Understanding Your Results

Principal vs Interest Chart

Shows how much of your final amount is principal versus interest earned.

Balance Growth

Line chart of your balance over time. Steeper curve with compound interest.

Rule of 72

Divide 72 by your interest rate to estimate years to double. At 7%%, money doubles in about 10 years.

Formulas Used

Simple interest:

I = P × r × t   |   A = P + I

Compound interest:

A = P(1 + r/n)^(n×t)

n = compoundings per year, t = time in years

Important Notes

  • This calculator is for educational and informational purposes only. It is not a substitute for professional financial advice.
  • Results are projections. Actual returns vary. Past performance does not guarantee future results.

When Simple Interest Applies

Some loans (e.g. short-term personal loans) use simple interest. You pay interest only on the principal, not on accrued interest.

When Compound Interest Applies

Savings accounts, CDs, and most investments compound. More frequent compounding (e.g. daily) yields slightly higher returns.

Interest Tips

  • For savings, look for accounts with daily compounding to maximize returns.
  • The Rule of 72: Divide 72 by your interest rate to estimate years to double.
  • Start saving early — time is the most powerful factor in compound growth.
  • For loans, prefer simple interest when available to pay less over time.

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