Flat vs Reducing Interest Rate

Introduction

A loan advertised at a lower interest rate may not always be the less expensive option. The final cost depends not only on the percentage shown but also on how the lender calculates interest.

Under the flat-rate method, interest is calculated on the original principal for the entire tenure. Under the reducing-balance method, interest is charged only on the outstanding principal, which falls after every EMI. As a result, a flat rate and a reducing rate with the same headline percentage do not produce the same interest cost.

This guide explains both methods, compares their formulas and uses a simple example to help borrowers evaluate a loan more accurately.

What Is a Flat Interest Rate?

A flat interest rate is calculated on the full original loan amount throughout the loan tenure. Repayment of principal through monthly EMIs does not reduce the amount used for calculating interest.

For example, if a borrower takes a loan of ₹1,00,000 for two years at a flat rate of 12% per annum, interest is calculated on ₹1,00,000 for both years—even though part of the principal is repaid every month.

Flat interest formula

Total interest = Principal × Annual interest rate × Loan tenure

EMI = (Principal + Total interest) ÷ Number of monthly instalments

What Is a Reducing Interest Rate?

A reducing or diminishing balance interest rate is calculated on the principal outstanding after each EMI. Every EMI normally contains a principal component and an interest component. Once the principal component is paid, the outstanding balance decreases and the next month’s interest is calculated on that lower amount.

During the initial part of the tenure, a larger portion of the EMI generally goes towards interest. As repayment progresses, the interest component falls and the principal component rises, while the EMI may remain unchanged for a standard fixed-rate loan.

Reducing-balance EMI formula

EMI = P × r × (1 + r)ⁿ ÷ [(1 + r)ⁿ − 1]

Here, P is the principal, r is the monthly interest rate and n is the total number of monthly instalments.

Flat vs Reducing Interest Rate Example

Consider an illustrative loan of ₹1,00,000 for 24 months. Both options display an annual interest rate of 12%. Processing fees, GST and other charges are excluded so that only the calculation methods can be compared.

In this example, the reducing-balance loan costs approximately ₹11,024 less in interest even though both loans display 12%. The difference arises because the flat-rate loan keeps charging interest on the original ₹1,00,000, while the reducing-balance loan charges interest on a declining amount.

The figures are rounded and illustrative. Actual EMI and total cost may vary according to the lender’s calculation method, repayment schedule, fees and taxes.

Key Differences Between Flat and Reducing Rates

Why Can a Flat Rate Look Lower?

A flat rate can appear attractive because the displayed percentage may be smaller than the reducing rate offered by another lender. However, directly comparing these two percentages can be misleading because their calculation bases are different.

For a fair comparison, borrowers should check the annual percentage rate, or APR, along with the total interest, total repayment amount, EMI and applicable charges. APR represents the annual cost of credit and incorporates interest and specified charges under the applicable disclosure framework. It is more useful than the headline rate when comparing loan offers with different fee structures or calculation methods.

What Should You Check Before Choosing a Loan?

Calculation method: Confirm whether the quoted rate is flat or reducing.

APR: Compare the annual cost of different offers on a consistent basis.

Total amount payable: Check the combined amount of principal, interest and applicable charges.

EMI and tenure: Make sure the monthly payment is manageable without stretching the tenure unnecessarily.

Processing and other charges: Review processing fees, GST, late-payment charges, bounce charges and any other applicable cost.

Prepayment terms: Check whether part-payment or foreclosure is permitted and whether charges apply.

Key Facts Statement: Read the KFS before accepting the loan. It summarises important pricing and repayment information.

Which Interest Method Is Better?

At the same displayed annual rate and for the same amount and tenure, a reducing-balance loan normally results in lower interest because the outstanding principal declines over time. But borrowers should not select a loan using the calculation method alone.

A loan with a reducing rate can still cost more if it carries a much higher rate or substantial fees. Similarly, an offer with a flat rate should be assessed using its equivalent annual cost, APR and total repayment amount. The better option is the one that offers a manageable EMI and the lower overall cost after every applicable charge is included.

Conclusion

Flat and reducing interest rates may use the same percentage but produce very different borrowing costs. A flat rate applies to the original principal for the full tenure, whereas a reducing rate applies to the outstanding balance after each repayment.

Before accepting a personal loan, compare the APR, EMI, total amount payable, charges and prepayment conditions—not just the advertised rate. A few minutes spent reading the Key Facts Statement and repayment schedule can prevent an expensive comparison mistake.