Simple Interest Calculator: P x R x T (Free Online)

Simple interest is the most straightforward way to work out what a loan costs or a deposit earns: it is charged only on the original sum, never on past interest. This guide explains the P x R x T formula, walks through a worked example, and shows where simple interest applies. The Simple Interest Calculator gives you the interest and final total in seconds — free, instant and private in your browser, with no sign-up.

How simple interest works

Simple interest is calculated on the principal alone for the whole term. The formula is:

• I = P times R times T

Where I is the interest, P is the principal (the starting amount), R is the annual rate as a decimal, and T is the time in years. The final amount you owe or receive is P + I.

Unlike compound interest, simple interest does not earn interest on interest, so it grows in a straight line. That makes it easy to predict and common in short-term loans.

How to use the Simple Interest Calculator

Three inputs, instant result:

1. Open the Simple Interest Calculator.
2. Enter the principal amount.
3. Enter the annual interest rate as a percentage.
4. Enter the term in years (or months).
5. Read the total interest and the final amount.

It updates live as you change any value, so you can compare loan terms or rates side by side.

Worked example: 5,000 at 6% for 3 years

You deposit 5,000 at a 6% annual simple interest rate for 3 years.

Apply I = P times R times T, with R as a decimal:

• I = 5,000 times 0.06 times 3
• 5,000 times 0.06 = 300 per year
• 300 times 3 = 900

So the interest is 900, and the final amount is 5,000 + 900 = 5,900. Notice the interest is the same 300 each year because it is always based on the original 5,000.

Simple interest vs compound interest

The key difference is what the interest is calculated on. Simple interest uses only the principal; compound interest adds each period's interest to the balance, so future interest is larger.

For 5,000 at 6% over 3 years, simple interest gives 900. Compound interest, added yearly, gives about 955 — more, because year two earns interest on the first year's interest too. Over long periods the gap grows wide, which is why savings usually compound and short loans often use simple interest.

When simple interest is used

Simple interest appears in many short-term and fixed arrangements: some car loans and personal loans, certain bonds, short-term promissory notes, and basic finance coursework. It is also a quick way to estimate the cost of borrowing before fees. Knowing whether a product uses simple or compound interest helps you compare true costs and avoid surprises.

Tips and common mistakes

Calculate it correctly:

• Convert the rate to a decimal before multiplying — 6% is 0.06, not 6.
• Keep the time unit consistent with the rate; an annual rate needs the term in years.
• For a 6-month term, use 0.5 years.
• Simple interest understates the cost of long-term compounding debt, so do not assume a credit card works this way.

For compounding, use the Compound Interest Calculator; for monthly loan payments, the Loan Calculator. More are in the free calculators.

Is it private?

Yes. The Simple Interest Calculator runs entirely in your browser, so the amounts and rates you enter are never uploaded or stored. There is no account and no tracking, and it works offline once loaded. Discover more free, private tools for everyday money calculations.