Simple Interest Calculator

Work out the simple interest on a fixed principal, or solve for the rate or time needed, and see how the result compares with compound interest over the same term.

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What do you want the calculator to work out?
Advanced: currency symbol
Interest earned
0
Enter the figures above to see a result.
Principal0
Interest0
Final total0
Principal versus interest
Principal Interest

The bar splits the final total into the money you started with and the interest added on top.

Year-by-year accumulated interest
End of yearInterest that yearTotal interest so farBalance

With simple interest the same amount is added every full year, because it is always a percent of the original principal and never of the growing balance.

Simple interest versus compound interest
MethodInterestFinal total

Compound interest also charges interest on interest already added, so over the same term it produces a larger total. The gap row shows how much extra compounding would add.

For beginners: how to read this result
The formula in plain wordsInterest equals principal multiplied by the annual rate as a fraction multiplied by the time in years. So 10,000 at 5% for 3 years earns 10,000 times 0.05 times 3.
Interest stays on the original amountSimple interest is always a percent of the starting principal. It does not grow as the balance grows, which is why each full year adds the same amount.
Three modes solve for different unknownsPick the mode for the number you do not know: the interest, the rate, or the time. The field being solved for disappears from the inputs.
Compound interest is differentCompound interest adds interest on top of earlier interest. The comparison table shows the gap so you do not confuse the two methods.
This is an estimate based on the figures you enter and uses the simple-interest method, where interest is charged on the original principal only. It does not account for compounding inside the headline result, inflation, tax on interest, fees, day-count conventions or irregular payments. Real loan and deposit terms vary, so check the conditions of your own agreement before relying on this figure.

To get a result, choose one of the preset scenarios or enter your own figures. Simple interest is charged on the original principal only and never on interest already added, which is what separates it from compound interest.

The three modes

The mode toggle changes which field the calculator solves for, and the field being solved for disappears from the inputs.

  • Interest earned — you enter the principal, the annual rate and the time. The calculator returns the interest and the final total. The target-interest field is hidden.
  • Required rate — you enter the principal, a target interest amount and the time. The calculator returns the annual rate needed. The rate field is hidden.
  • Required time — you enter the principal, the annual rate and a target interest amount. The calculator returns the time needed. The time field is hidden.

The formula in plain English

Simple interest equals the principal multiplied by the annual rate, written as a fraction, multiplied by the time in years. For example, a principal of 10,000 at an annual rate of 5 percent for 3 years earns 10,000 times 0.05 times 3, which is 1,500. The final total is the principal plus the interest. To solve for the rate, divide the target interest by the principal multiplied by the time; to solve for the time, divide the target interest by the principal multiplied by the rate fraction.

Year-by-year ledger and the compound comparison

The year-by-year table shows the interest added each full year and the running balance. Because simple interest is always a percent of the original principal, every full year adds exactly the same amount. The comparison table places the simple-interest result next to what yearly compound interest would produce over the same term, with a gap row showing the extra amount compounding would add.

What is not included

This calculator uses the simple-interest method only. The headline result does not compound. It does not account for inflation, tax on interest, account or loan fees, day-count conventions such as 30/360 or actual/365, or irregular payments and withdrawals. Real loan and deposit agreements vary, so treat the result as a planning guide and confirm the terms of your own agreement.