How to Calculate Loan Interest – Simple & Reducing Balance Methods
Loan interest is the cost of borrowing money, and understanding how banks calculate it can save you lakhs over the life of a loan. This guide covers both the simple interest method and the reducing balance method used by Indian banks, with clear formulas and worked examples.
Two Methods of Loan Interest Calculation
Indian banks and lenders use two fundamentally different methods: the Flat Rate (simple interest on original principal) and the Reducing Balance (interest on outstanding principal). Most home loans, car loans, and personal loans use reducing balance. Some short-term loans and some NBFCs use flat rate — which is significantly more expensive for the borrower despite appearing lower.
Method 1: Flat Rate (Simple Interest)
Total Interest = Interest Per Year × Years
Monthly Payment = (Principal + Total Interest) / Total Months
Example: ₹2,00,000 loan at 7% flat rate for 2 years:
- Annual Interest = ₹2,00,000 × 7% = ₹14,000
- Total Interest = ₹14,000 × 2 = ₹28,000
- Monthly Payment = (₹2,00,000 + ₹28,000) / 24 = ₹9,500/month
Method 2: Reducing Balance (Banks Use This)
EMI = [P × r × (1+r)^N] / [(1+r)^N − 1]
Total Interest = (EMI × N) − Principal
Same loan under reducing balance: ₹2,00,000 at 7% for 2 years (24 months):
- Monthly rate r = 7/12/100 = 0.005833
- EMI = [2,00,000 × 0.005833 × (1.005833)^24] / [(1.005833)^24 − 1]
- = [2,00,000 × 0.005833 × 1.1499] / [0.1499]
- EMI = ₹1,340.33 / 0.1499 = ₹8,943/month
- Total Interest = (₹8,943 × 24) − ₹2,00,000 = ₹14,632
Comparison: Flat rate costs ₹28,000 in interest. Reducing balance costs ₹14,632 — nearly half!
The Key Principle: Interest Decreases Every Month
Month 1: Interest = ₹2,00,000 × 0.5833% = ₹1,167. Principal repaid = ₹8,943 − ₹1,167 = ₹7,776. Remaining balance = ₹1,92,224.
Month 2: Interest = ₹1,92,224 × 0.5833% = ₹1,121. Principal repaid = ₹8,943 − ₹1,121 = ₹7,822. And so on...
The interest amount decreases every month as you repay principal — this is why prepayments in the first few years save the most interest.
How to Reduce Total Loan Interest
- Negotiate a lower rate (0.5% lower on ₹50L home loan saves ~₹5-8L over 20 years)
- Make prepayments — even ₹10,000 extra in Year 1 can save ₹30,000-50,000 in total interest
- Choose shorter tenure if affordable — 15 years vs 25 years on a ₹30L loan saves ~₹28L in interest
- Maintain high CIBIL score (750+) to qualify for lowest available rates
Frequently Asked Questions
What's a good interest rate for personal loans in India?
Personal loan rates in India range from 10.5% to 24% p.a. Banking customers with 750+ CIBIL scores can often get rates below 12%. NBFCs typically charge 14-24%.
Is 7% flat rate the same as 7% reducing balance?
No! A 7% flat rate is equivalent to approximately 13% reducing balance rate. Always clarify which method the lender uses. RBI mandates that banks disclose the Annual Percentage Rate (APR) which reflects the true cost of credit.
🔢 Compute instantly: Loan Interest Calculator, EMI Calculator, Loan Affordability Calculator.
Try it yourself — Free & Instant
No signup required. Results in seconds.
Open Loan Interest Calculator →