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Simple Interest Calculator

Calculate simple interest on your investments or loans quickly.

Result

Principal₹10,000
Total Interest₹2,500
Total Amount₹12,500

Formula

Simple Interest = (Principal × Rate × Time) / 100

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Updated: May 2026

Simple Interest

Simple Interest is the easiest way to calculate interest charge on a loan. It is determined by multiplying the daily interest rate by the principal by the number of days that elapse between payments.

Formula

SI = (P * R * T) / 100
Where P = Principal, R = Rate per annum, T = Time in years.

How to Use the Simple Interest Calculator

Enter the principal amount, annual interest rate, and time period. The calculator shows the simple interest earned or payable, along with the total amount at the end of the period.

Simple interest is useful when interest is charged only on the original principal and does not compound. This makes it easier to understand than compound interest, but it is less common in long-term investment products.

Simple Interest Formula Explained

Simple Interest = (Principal x Rate x Time) / 100

Total amount is:

Total Amount = Principal + Simple Interest

For example, if you invest ₹1,00,000 at 8% simple interest for 3 years:

SI = 1,00,000 x 8 x 3 / 100 = ₹24,000

The total amount will be:

₹1,00,000 + ₹24,000 = ₹1,24,000

Simple Interest vs Compound Interest

FeatureSimple InterestCompound Interest
Interest baseOriginal principal onlyPrincipal plus accumulated interest
GrowthStraight-lineAccelerating
CalculationEasierMore powerful over time
Best forShort-term loans or basic interest estimatesLong-term investments

If you are planning long-term savings, compound interest is usually more relevant. If you are checking a short-term loan, delayed payment, or basic interest charge, simple interest may be enough.

When Simple Interest is Used

Simple interest may be used in some personal loans, short-term lending, informal borrowing, invoice delays, late payment charges, and educational examples. It is also useful for quickly estimating the cost of borrowing before looking at more detailed EMI schedules.

Common Mistakes to Avoid

  1. Do not confuse monthly rate with annual rate.
  2. Convert months into years before using the formula.
  3. Remember that simple interest does not add interest back to principal.
  4. For EMIs, use an EMI calculator instead of simple interest.
  5. For FDs, PPF, or investment growth, use a compound interest calculator.

Frequently Asked Questions

What is simple interest?

Simple interest is interest calculated only on the original principal amount.

Why is simple interest lower than compound interest?

Simple interest does not reinvest earned interest. The calculation base remains the original principal for the full tenure.

Is simple interest better than compound interest?

For borrowers, simple interest is usually cheaper. For investors, compound interest usually creates more wealth over time.

Can simple interest be used for FD returns?

Most cumulative FDs use compound interest, so an FD calculator is more accurate.

How do I calculate simple interest monthly?

Convert the time period into years. For example, 6 months is 0.5 years.

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