Simple Interest Calculator
Calculate simple interest and the final amount from principal, annual rate and time. Interest = principal × rate × time.
The selected field is calculated from I = P × r × t.
Compound comparison assumption: annual compounding. Non-whole years use the fractional exponent (1 + r)t as an annual-compounding approximation, not a day-count calculation.
Timeline with annual compound comparison
Long-term growth? Compound interest · installment loans: Loan calculator · Indian FD: FD calculator.
Simple interest, solved four ways
Use I = P × r × t to calculate interest or rearrange it to solve principal, annual rate or time. The comparison column is explicitly annual compounding, not a claim about a specific loan or bond convention. For date-based products, confirm the lender's day-count rule; use the compound interest calculator when you need another compounding frequency.
FAQ
What is the simple interest formula?
Interest = Principal × Rate × Time, where rate is annual and time is in years. The total is principal plus interest.
Can it solve for any variable?
Yes. Choose interest (I), principal (P), annual rate (r) or time (t). The selected field is calculated from I = P × r × t while the other three fields remain editable.
How is the compound comparison calculated?
The comparison uses annual compounding by default: P × (1 + r)^t. Simple interest is still calculated only on the original principal, while the annual compound comparison reinvests accumulated interest.
How are non-whole years handled?
Enter time in years; for example, six months is 0.5 years. For a non-whole year, the compound comparison uses the fractional exponent (1 + r)^t as a fractional-year annual-compounding approximation. It does not apply an ACT/365, ACT/360 or 30/360 day-count convention.
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