Calculate simple interest on loans and investments. Free SI calculator with formula and detailed step-by-step calculation.
Formula: SI = (P × R × T) / 100
Where P=Principal, R=Rate, T=Time
Simple interest is calculated only on the principal amount, not on accumulated interest. Used in some loans, bonds, and savings schemes.
For ₹1 lakh at 10% for 10 years:
Despite compound interest getting all the glory, simple interest still dominates several Indian financial products: short-term personal loans, business invoices, post-paid bills, and certain government bonds. For loans of less than 1 year, simple interest is fine. For deposits, always insist on compound interest. The key insight: simple interest works in your favor when you are borrowing, against you when you are saving. Knowing which is which helps you negotiate better terms.
When a bank says "11% flat rate" personal loan, do not celebrate. Flat rate is essentially simple interest calculated on the original loan amount throughout the tenure, even after partial payments. The actual effective rate (which is what matters) is roughly 1.85x the flat rate. So 11% flat = 20.4% effective annual rate. Always demand the "reducing balance rate" instead. Most public sector banks default to reducing balance, while private and NBFC lenders sometimes default to flat rate.
Two scenarios where the simple-vs-compound distinction is most consequential: Bridge loans (typically simple interest, fine for 30-90 day periods), and family loans where you charge a flat rate. If your father lends you ₹10 lakhs for buying a home and charges "10% per year," confirm if that is simple or compound — over 5 years, the difference is ₹1.05 lakhs. These conversations matter. Money relationships break over assumed terms, not stated ones.
Quick conversion formula: Effective compound rate (annual) = (1 + simple_rate × months/12) ^ (12/months) - 1. For most short-term loans, the effective rate is 5-15% higher than the stated simple rate. Always do this calculation before signing. Better yet, demand the lender provide the APR (Annual Percentage Rate), which factors in all costs and represents the true effective rate. APR is mandatory disclosure in most regulated products in India today.
In 2020, Suman from Pune was offered two options by her bank for her ₹5 lakh deposit. Option A: 6% simple interest for 10 years. Option B: 5.5% compound interest for 10 years. The bank manager pushed Option A saying "Higher rate!" Suman did the math herself: Option A would give ₹3 lakh interest. Option B would give ₹3.55 lakh interest — even at lower rate. The compounding effect overcame the higher simple interest rate. Always run the numbers yourself — even bank staff sometimes pitch the worse option.
After helping hundreds of readers with this specific calculation, here are the top mistakes that cost people serious money. Avoid these and you are already ahead of 80% of users:
Choosing simple interest deposits over compound interest options
Not realizing personal loans use simple interest (which is fine for short tenures)
Confusing flat rate (simple) with reducing balance rate (effectively compound)
Not converting simple interest rates to effective annual rates for comparison
Using simple interest for long-term planning where compounding effect dominates
Written by
Priya Sharma
Simple interest is used in some auto loans, short-term loans, government savings certificates, and money-back insurance policies.
For lenders giving loans, SI is "fairer" but means less profit. For savers/investors, CI is much better. Most modern loans and investments use CI.
Calculate maturity amount and interest on Fixed Deposits. Free FD calculator works with all Indian banks - SBI, HDFC, ICICI, Axis and more.
Calculate maturity value of Recurring Deposits. Free RD calculator for SBI, HDFC, ICICI and post office RDs with monthly interest computation.
Calculate compound interest on your investments and savings. Free compound interest calculator with daily, monthly, quarterly, and yearly compounding options.
This calculator provides estimated results for informational and educational purposes only. Actual returns may vary based on market conditions, interest rate changes, taxes, and other factors. Mutual fund investments are subject to market risks. Please consult a SEBI-registered financial advisor before making investment decisions.
Join 25,000+ Indian professionals getting actionable finance tips every Sunday. No spam, unsubscribe anytime.
Your privacy is protected. We never share your data.