Math
Calculate interest and total amount using the simple interest formula — instant result.
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Lending ₹50,000 at 9% simple interest for 4 years: SI = (50,000 × 9 × 4) / 100 = ₹18,000. Total repayment = ₹50,000 + ₹18,000 = ₹68,000. Notice the interest is the same ₹4,500/year for all 4 years — unlike compound interest, where each year's interest would be calculated on a growing balance.
Because simple interest is always calculated on the original principal — never on previously earned interest — the interest amount is identical every single period, which makes it easy to predict and easy to verify by hand. That predictability is exactly why it's less common for long-term loans and investments, where compound interest generally benefits the lender or investor more over time — but it remains useful for short-term, transparent calculations.
SI = (P × R × T) / 100, where P is the principal, R is the annual interest rate as a percentage, and T is time in years. The total amount is the principal plus the simple interest: A = P + SI.
Simple interest is calculated only on the original principal for every period — it never grows. Compound interest is calculated on the principal plus all previously earned interest, so it grows faster over time. For the same rate and term, compound interest always produces a higher (or equal) return.
Some short-term loans, certain bonds, and basic interest calculations on things like car loans (in some structures) use simple interest. It's also the standard starting point for teaching interest math, since the formula is more transparent than compound interest.