EMI vs Flat Interest Rate
Understand two common ways loan interest can be expressed or calculated, and why the same advertised rate can lead to different borrowing costs.
When comparing loans, the interest rate alone does not always tell you how much the loan will cost. The method used to calculate interest can make a significant difference to the total interest paid and the monthly repayment.
Two terms you may encounter are EMI on a reducing balance and a flat interest rate. They describe different ways of calculating loan interest, so it is important to understand the underlying calculation before comparing offers.
Quick comparison
With a reducing-balance EMI, interest is calculated on the outstanding loan balance. With a flat-rate calculation, interest is calculated on the original principal throughout the stated tenure.
What Is EMI?
EMI stands for Equated Monthly Instalment. It is a fixed periodic payment used to repay a loan over a specified tenure. A typical EMI contains both a principal component and an interest component.
For a standard reducing-balance loan, the interest portion is calculated using the outstanding principal. As principal is repaid, the outstanding balance generally falls, so the interest charged in later periods can also fall.
EMI Formula
EMI = P × r × (1 + r)n ÷ [(1 + r)n − 1]
P = principal • r = monthly interest rate • n = number of monthly instalments
For a monthly EMI calculation, an annual interest rate is generally converted to a monthly rate according to the assumptions of the loan calculation. The tenure is expressed as the number of monthly instalments.
What Is a Flat Interest Rate?
Under a flat-rate method, interest is calculated using the original principal for the stated loan period rather than recalculating interest on the declining outstanding balance after each repayment.
Flat Interest = P × R × T ÷ 100
P = principal • R = annual flat rate • T = tenure in years
The total repayment under a flat-rate method can then be determined by adding the calculated interest to the original principal and dividing the total by the number of repayment periods when the repayments are equal.
EMI vs Flat Interest: Key Difference
| Feature | Reducing-Balance EMI | Flat Interest |
|---|---|---|
| Interest base | Outstanding principal | Original principal |
| Outstanding balance | Changes as principal is repaid | Not used to reduce the interest base in the same way |
| Interest over time | Generally declines as principal is repaid | Based on the original principal |
| Rate comparison | Cannot be compared directly with a flat rate without considering the calculation method | May look lower but can represent a different borrowing cost |
Example: Reducing-Balance EMI
Suppose a loan has a principal of ₹1,00,000, an annual interest rate of 12%, and a tenure of 2 years.
Using the standard reducing-balance EMI formula, the monthly EMI is approximately ₹4,707.35. Total payments over 24 months are approximately ₹1,12,976.40, so the total interest is approximately ₹12,976.40.
Example: Flat Interest Rate
Using the same principal of ₹1,00,000 and a 12% annual flat interest rate for 2 years:
Although the examples use the same principal, annual percentage and tenure, the calculated borrowing cost differs because the interest is applied differently.
Why a Flat Rate and EMI Rate Should Not Be Compared Directly
A flat interest rate and a reducing-balance interest rate use different interest bases. A flat rate continues to reference the original principal, while a reducing-balance calculation uses the outstanding principal.
For this reason, a lower flat-rate percentage does not automatically mean a cheaper loan than a higher reducing-balance rate. The correct comparison should consider the total repayment, total interest, fees, tenure and other loan conditions.
Which Calculation Should You Use?
Use EMI Calculation
Use a reducing-balance EMI calculation when your loan specifies an outstanding-balance interest method and monthly instalments.
Use Flat Interest Calculation
Use a flat-rate calculation when the lender explicitly states that interest is charged as a percentage of the original principal for the loan tenure.
How to Compare Loan Offers
Check the interest method
Confirm whether the rate is flat, reducing balance or another method.
Calculate total interest
Look beyond the headline rate and calculate the total interest payable over the full tenure.
Include fees
Consider processing fees, prepayment charges and other applicable costs.
Compare total repayment
The total amount paid over the loan tenure provides a more useful comparison than the rate alone.
Calculate your EMI
Use the Numorify EMI Calculator to estimate your monthly payment, total interest and total repayment.
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