Simple Interest Calculator

Simple interest is I = P × r × t, with the annual percentage divided by 100 before multiplication. For principal 1,000, annual rate 5% and five years, interest is 250 and the maturity balance is 1,250. The period table starts at zero accrued interest and ends at the same maturity total.

Each complete equal-length period accrues the same interest. A final partial period accrues only its fraction. The principal series stays flat; the simple-interest balance adds accrued interest without charging interest on that interest.

Consumer simple-interest loans may calculate charges on outstanding principal as it changes. This tool instead keeps the original principal unchanged. Dividing the maturity total across months is an allocation illustration, not a lender payment or amortization schedule.

Use the linked Loan Repayment calculator for a declining-balance schedule. This model cannot measure savings from extra payments, early payoff, payment dates or a lender’s allocation rules. A currency change alters the denomination only and does not convert money.

Years are used as entered; months are divided by 12. In those modes calendar dates label the schedule without changing interest. End-of-month dates stay anchored to the original day, clipped to the last available day. A fractional month interpolates between anchored dates and rounds only the calendar label to a day.

Days and date ranges use actual elapsed whole days divided by the selected fixed 365 or 360. The start is excluded and the end included; leap days count normally. These are explicit calculator conventions, not a representation of every financial contract. Zero time has one initial point and zero interest. A zero divisor in an inverse calculation can be indeterminate or infeasible.

The compound line uses the same principal, nominal annual rate and horizon: P × (1 + r/n)^(n×t). The selected frequency is n. A fractional exponent interpolates compound growth within a period. Consequently, annual compounding over less than one year can produce a lower total than simple interest at the same nominal rate; the verdict follows the calculated totals.

The 1%, 5% and 10% presets and rate scenarios are editable illustrations dated 2026-10-18, not market quotes or forecasts. Inflation discounts the ending simple balance into starting-date purchasing power. Fees, taxes, cash flows and investment risk are not modeled. CSV contains the same accrual rows as the chart and table. Sharing first shows a disclosure preview and leaves the current address unchanged.