What formula does simple interest use?

Simple interest uses SI = P × R × T / 100, where P is principal, R is the annual interest rate percentage, and T is time in years.

How do I calculate simple interest per annum?

Use the annual rate as R and write time in years. For example, 10,000 at 12% per annum for 2 years gives 10,000 × 12 × 2 / 100 = 2,400 interest.

How are months handled in the formula?

Months are converted into years. Six months becomes 0.5 years, so simple interest for 6 months is half of one year at the same annual rate.

What is the total amount?

Total amount is principal plus simple interest. If the principal is 10,000 and the interest is 2,400, the total amount is 12,400.

When should I use compound interest instead?

Use compound interest when interest is periodically added to the balance and then earns interest itself, such as monthly, quarterly, or daily compounding.

FREE ONLINE SIMPLE INTEREST CALCULATOR

Simple Interest Calculator for Principal, Rate, and Time

Calculate simple interest per annum, interest earned, and total amount using the standard principal × rate × time formula. Use it for quick study examples, finance homework, savings estimates, and basic interest formula checks.

CALCULATE INTEREST

Enter principal, annual rate, and time.

Principal amountAnnual interest rate (%)TimeTime unit

SIMPLE INTEREST FORMULA

Interest = Principal × Rate × Time / 100Rate is treated as an annual percentage rate. Months and days are converted into years before the formula is applied.

TRY AN EXAMPLE

HOW TO CALCULATE SIMPLE INTEREST

Understand the formula before using the result.

Simple interest does not add previous interest back into the balance. It uses the original principal, the annual rate, and the length of time. That makes it useful for basic interest formula problems and clear per-annum examples.

PRINCIPAL

The starting amount

Principal is the original amount of money. In the formula, it is the value that earns interest.

RATE PER ANNUM

The annual percentage rate

Per annum means per year. A 12% per annum rate means 12% for one full year, 6% for six months, and about 3% for three months under simple interest.

TIME

Convert months or days into years

If the time is given in months, divide by 12. If the time is given in days, divide by 365 unless your class or lender uses a different day-count rule.

WORKED EXAMPLE

How to calculate simple interest per annum.

Suppose the principal is 10,000, the rate is 12% per annum, and the time is 2 years. Multiply the values exactly in the formula, then add the interest to the principal to get the total amount.

01P = 10,000Start with the principal.

02R = 12%Use the annual rate as a percentage.

03T = 2 yearsKeep time in years.

04SI = 10,000 × 12 × 2 / 100 = 2,400Total amount = 12,400.

USE SIMPLE INTEREST WHEN

The interest is not reinvested

School formula questions use SI = PRT / 100.
The problem says simple interest or flat interest.
You only need interest earned on the original principal.

USE COMPOUND INTEREST WHEN

Interest earns more interest

The balance grows after each compounding period.
The question mentions monthly, quarterly, or daily compounding.
You need future value with repeated reinvestment.

This calculator is for education and basic planning. Real accounts, loans, taxes, fees, and lender rules can use different rounding or day-count methods, so check official terms before making financial decisions.

Simple Interest Calculator

Use principal, annual rate, and time in years, months, or days to calculate simple interest, interest earned, final amount, and a clear formula breakdown.

Simple interest formula: SI = P × R × T / 100

Interest earned from a principal amount and annual rate

Simple interest per annum with years, months, or days

Total maturity amount after adding interest to principal

KEY FUNCTIONS

Principal, annual rate, and time inputsYears, months, or days converted into formula timeInterest earned and total amountFormula line showing principal × rate × time / 100Worked per-annum example and simple vs compound comparison

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