Simple interest calculator
Calculate simple interest and the final amount from principal, rate and time.
Final amount
$1,120.00
Interest$120.00
Principal$1,000.00
In simple interest, interest always applies to the initial principal (unlike compound interest).
How the calculation works
Simple interest grows linearly: I = P × r × t and Amount = P + I, where r is the rate per period and t the number of periods.
Frequently asked questions
When is simple interest used?
In some short-term contracts and fines. Most investments and loans use compound interest.
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Updated on June 17, 2026 · by Rafael Rossi · Methodology & sources