What is a Simple Interest Calculator?

A Simple Interest Calculator is a free financial tool that computes interest earned or payable on a principal amount at a fixed rate over a specified period. Unlike compound interest, simple interest is calculated only on the original principal — never on accumulated interest. This makes it straightforward to compute and commonly used for short-term loans, fixed deposits, and certain types of bonds.

Simple Interest vs Compound Interest

The key difference is that simple interest is calculated only on the principal, while compound interest is calculated on the principal plus previously earned interest. For example, ₹10,000 at 10% for 3 years earns ₹3,000 in simple interest but ₹3,310 in compound interest. Simple interest is predictable and linear, making it easier to plan, while compound interest grows exponentially over time.

Simple Interest Formula

The formula is SI = (P × R × T) / 100, where P = Principal amount, R = Annual interest rate (%), and T = Time period in years. Total Amount = Principal + Simple Interest. For example, ₹50,000 at 8% for 5 years gives: SI = (50000 × 8 × 5) / 100 = ₹20,000. Total = ₹70,000. Simple, predictable, and easy to calculate.