WiseCalcs

Simple interest calculator

Enter the starting amount, the annual interest rate, and the number of years. The calculator shows the total interest and the final balance as you type.

Use it to find the simple interest earned on a principal and the final balance after a set number of years.

USD
%
yr

Final balance

$1,150.00

Principal Interest

Total interest: $150.00

The result updates as you type. The bar splits the final balance into your original principal and the interest it earned.

How does it work?

Interest is charged only on the original principal, never on accumulated interest. With a 0% rate the balance is simply the principal.

Simple interest formula

I=P×r100×tA=P+I\begin{aligned} &I = P \times \tfrac{r}{100} \times t\\[2pt] &A = P + I \end{aligned}
I
Total interest earned.
A
Final balance (principal plus interest).
P
Starting principal.
r
Annual interest rate as a percentage.
t
Term in years.

1,000 at 5% for 3 years earns 150 in interest, for a final balance of 1,150.

Method & sources

Interest is charged only on the original principal, never on accumulated interest. The rate is the same every year and you choose it yourself; the calculator does not look up market rates. The currency shown follows the site language; the interest math is the same in every market.

Sources

Where this method comes from — use these references to understand the formula, assumptions, and limits.

How we calculate

  • Interest is charged only on the original principal, never on accumulated interest.
  • The rate is the same every year and you choose it yourself; the calculator does not look up market rates.
  • The currency shown follows the site language; the interest math is the same in every market.
  • Taxes, fees, and inflation are not included.

Rounding

Balances are rounded to two decimals for display. The calculation uses full precision.

What this calculator does

Simple interest is charged only on the original amount you start with. This calculator multiplies the principal by the annual rate and the number of years to find the total interest, then adds it to the principal for the final balance.

How to use it

  1. Enter the starting amount (the principal).
  2. Enter the annual interest rate as a percentage.
  3. Enter the number of years.
  4. Read the total interest and the final balance below.

A worked example

1,000 at 5% for 3 years earns 1,000 × 5% × 3 = 150 in interest, for a final balance of 1,150.

Simple interest vs compound interest

Simple interest is always calculated on the original principal, so the interest earned is the same every year. Compound interest also earns interest on the interest already added, so it grows faster over time. For longer terms, use the compound interest calculator instead.

Common mistakes

  • Entering a rate that is already a decimal. Use 5 for 5%, not 0.05.
  • Expecting the balance to grow faster each year. With simple interest the yearly interest is constant.
  • Confusing the interest with the final balance. The final balance is the principal plus the interest.

When it's useful

Short-term loans, some bonds and savings products, and quick estimates where interest is not compounded.

FAQ

How do I calculate simple interest?
Multiply the principal by the annual rate divided by 100, then by the number of years. 1,000 at 5% for 3 years earns 150.
What is the difference between the interest and the final balance?
The interest is what the amount earns; the final balance is the original principal plus that interest.
How is simple interest different from compound interest?
Simple interest is always charged on the original principal only. Compound interest also earns interest on interest already added, so it grows faster over time.
Does this include tax or inflation?
No. The calculator works on the principal, rate, and years only. Taxes, fees, and inflation are not included.
Which currency does it use?
The currency follows the site language. The interest math is identical in every market.
Can I share a calculation?
Yes. Use Share to copy a link that reopens the calculator with the same amount, rate, and years.

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<iframe src="https://wisecalcs.com/embed/en/simple-interest-calculator" width="100%" height="520" style="border:0" loading="lazy"></iframe> <p>Calculator from <a href="https://wisecalcs.com/en/investments-retirement/simple-interest">WiseCalcs</a></p>