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💰 Simple Interest Calculator

Calculate simple interest on any loan or investment instantly. Enter your principal, annual interest rate, and time period to see the interest earned and total amount due.

Simple Interest Formula

SI = P × R × T ÷ 100
P = Principal amount R = Rate of interest (%) T = Time period (years)

Total Amount = P + SI. Interest is calculated only on the original principal — it does not compound.

How to Calculate Simple Interest — Step by Step

  1. 1
    Enter the Principal
    Type the initial amount of money borrowed or invested.
  2. 2
    Enter the Annual Rate
    Enter the interest rate per year as a percentage (e.g., 8 for 8%).
  3. 3
    Enter the Time Period
    Enter the duration in years. For months, divide by 12 (e.g., 6 months = 0.5).
  4. 4
    Read Your Results
    The calculator instantly shows simple interest, total amount, and effective annual rate.

Real-World Example

You lend $5,000 at 8% per year for 3 years.

SI = $5,000 × 8 × 3 ÷ 100
SI = $1,200
Total Amount = $5,000 + $1,200 = $6,200
Effective Rate = 8% per year (unchanged, as SI is linear)

Frequently Asked Questions

Simple interest is calculated only on the original principal amount throughout the loan or investment period. Unlike compound interest, it does not add earned interest back to the principal. The formula is SI = P × R × T ÷ 100, making it predictable and easy to calculate.

Simple interest is commonly used for short-term loans, car loans, personal loans, and some savings accounts. It is also used in Treasury bills and certificates of deposit. Consumer loans like auto loans in the US often use simple interest because payments are applied first to accrued interest, then to principal.

With simple interest, you earn interest only on the principal. With compound interest, you earn interest on both the principal and any previously earned interest. For example, $10,000 at 10% for 5 years earns $5,000 in simple interest but $6,105 in compound interest (compounded annually).

Generally, yes. Borrowers pay less in total with simple interest compared to compound interest at the same rate over the same period, because interest does not accumulate on unpaid interest. However, the difference is smaller for short durations.

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