Calculate simple interest using SI = PRT/100 - find principal, rate or time, and compare with compound interest growth.
SI = PRT/100. Interest is always computed on the original principal. Used for short-term loans, vehicle loans (flat rate), chit funds, and NSC maturity.
CI = P[(1+r/n)^nt − 1]. Interest earns interest. Used for savings accounts, FDs, mutual funds, PPF - wherever reinvestment is automatic.
Car loans often advertised as "flat 9%" - actually ~16–17% effective. Flat rate = SI on full principal; reducing balance = true EMI rate. Always compare effective rates.
Approximate rule: flat rate × 1.8 = effective reducing-balance rate. A 9% flat loan is roughly equivalent to 16.2% reducing balance for your EMI comparison.
Simple interest is the most straightforward method of calculating interest on a principal amount. The formula SI = (P x R x T) / 100 - where P is principal, R is annual rate of interest, and T is time in years - has been taught in Indian schools since at least the 19th century and appears in NCERT mathematics textbooks from Class 7 onwards. Unlike compound interest, simple interest does not accumulate interest on previously earned interest, making it easier to understand and calculate manually.
Simple interest is used in short-term personal loans from cooperative banks and credit societies, gold loans from non-banking financial companies (NBFCs) like Muthoot Finance and Manappuram, agricultural loans under the Kisan Credit Card scheme, and fixed deposits with some small finance banks. RBI regulations require lenders to disclose the annualised interest rate (APR), and for short-term instruments, simple interest and APR calculations are closely aligned. Moneylenders regulated by state money-lending acts also typically charge simple interest.
Simple and compound interest problems are standard topics in SSC CGL, IBPS PO, SBI Clerk, RRB NTPC, CAT, and UPSC CSAT quantitative aptitude sections. CBSE Class 8 and 10 mathematics curricula both include interest calculations. This calculator not only computes SI but also shows a comparison with compound interest for the same principal, rate, and time, helping students and users understand the difference between the two concepts clearly.