Simple Interest Calculator
Calculate simple interest or solve for principal, rate, or time.
Result
Fill in the fields above, then press Calculate.
Examples
Finding Interest
$10,000 at 5% for 3 years: I = $10,000 * 0.05 * 3 = $1,500. Total amount = $11,500.
Finding Rate
If you earned $600 interest on $4,000 over 2 years: r = $600 / ($4,000 * 2) = 7.5% per year.
Finding Time
How long to earn $750 interest on $5,000 at 6%? t = $750 / ($5,000 * 0.06) = 2.5 years.
Frequently Asked Questions
What is simple interest?
Simple interest is calculated only on the original principal amount. Unlike compound interest, the interest earned does not itself earn additional interest in subsequent periods.
When is simple interest used?
Simple interest is commonly used for short-term loans, auto loans, some personal loans, and Treasury bills. It is also used as a baseline comparison against compound interest.
How is simple interest different from compound interest?
With simple interest, you earn interest only on the original principal. With compound interest, you earn interest on both the principal and previously accumulated interest, which grows faster over time.
Can I solve for any variable?
Yes. This calculator can solve for Interest, Principal, Rate, or Time given the other three values. Select the variable you want to find from the "Solve For" dropdown.
Result
Your result appears here and follows you as you scroll.
Quick Tips
Double check your inputs. Ensure units match (e.g., inches vs cm).
Did you know?
Calculators are estimates. Consult professionals for critical decisions.