Flat and Reducing Rate of Interest: Key Differences You Should Know
A loan advertised at a 10% interest rate may not actually cost you 10%. In fact, two loans carrying the same interest rate can lead to vastly different repayment amounts simply because of how the interest is calculated. This happens because lenders can calculate interest using either the flat rate or the reducing rate of interest method.
In this article, learn the basics of flat and reducing rate of interest, how each works, and which option is generally more cost-effective for borrowers.
What is the Flat Rate of Interest?
A flat rate of interest is a method in which interest is calculated on the original principal amount throughout the loan tenure. The interest amount remains fixed even though the borrower gradually repays the principal through monthly instalments.
Flat Rate of Interest Formula
Total Interest = (Principal × Rate × Tenure) ÷ 100
Where:
- Principal = Original loan amount
- Rate = Annual interest rate
- Tenure = Loan period in years
Example of Flat Rate of Interest
Suppose you take a loan of Rs 5,00,000 for three years at a flat interest rate of 10%.
Total Interest
= Rs 5,00,000 × 10% × 3
= Rs 1,50,000
Total Repayment
= Rs 5,00,000 + Rs 1,50,000
= Rs 6,50,000
Although the outstanding principal decreases with every EMI, the interest is still charged on the original Rs 5,00,000 for the entire tenure.
What is the Reducing Rate of Interest?
A reducing rate of interest, also known as the diminishing balance interest rate, calculates interest only on the outstanding loan amount.
As the borrower pays EMIs, the principal balance decreases. Consequently, the interest charged during subsequent months also decreases.
This method ensures that borrowers pay interest only on the amount they still owe.
How Reducing Interest Works
Month 1:
Outstanding Principal = Rs 5,00,000
Interest is calculated on Rs 5,00,000.
After several EMIs:
Outstanding Principal = Rs 4,00,000
Interest is now calculated on Rs 4,00,000.
As the loan balance reduces, the interest amount also declines.
What is the Difference Between Flat and Reducing Rate of Interest
A flat interest rate charges interest on the entire original loan amount throughout the loan tenure, even as you keep repaying the principal. On the other hand, a reducing interest rate charges interest only on the remaining outstanding loan balance, so the interest amount decreases with every EMI.
| Basis | Flat Interest Rate | Reducing Interest Rate |
| Interest Calculation | Calculated on the original loan amount throughout the tenure | Calculated on the outstanding principal balance after each EMI |
| Interest Cost | Higher overall borrowing cost | Lower total interest payable |
| Effective Rate | Significantly higher than the quoted rate | Generally close to the quoted interest rate |
| EMI Impact | Interest component remains fixed | Interest component declines with every EMI |
| Common Usage in 2026 | Primarily used for short-term loans, consumer durable financing and some vehicle loans | Widely used for home loans, personal loans, education loans and business loans |
| RBI Transparency Rules | Lenders must disclose the Annual Percentage Rate (APR) and effective borrowing cost through a Key Fact Statement (KFS) | Lenders must disclose APR and repayment details through a Key Fact Statement (KFS) |
| Prepayment Rules | Charges depend on the lender and the loan type | No foreclosure or prepayment charges on floating-rate loans to individual borrowers as per RBI guidelines |
| Benchmark Linkage | Usually offered as fixed-rate products | Most floating-rate loans are linked to External Benchmark Lending Rates (EBLR) and adjust with repo rate changes |
Know KFS’s meaning and purpose in detail!
Flat Rate to Reducing Rate Equivalency in 2026
| Flat Interest Rate | Approximate Equivalent Reducing Interest Rate |
| 8% Flat | 15% to 16% Reducing |
| 10% Flat | 18% to 20% Reducing |
| 12% Flat | 22% to 24% Reducing |
Example Comparing Flat and Reducing Rate of Interest
Consider a loan of Rs 10 lakh for five years.
Scenario 1: Flat Interest Rate
Interest Rate: 10%
Interest is charged on the full Rs 10 lakh for five years.
Total interest cost remains significantly higher because the lender ignores the fact that the borrower is gradually repaying the principal.
Scenario 2: Reducing Interest Rate
Interest Rate: 10%
Interest is charged only on the outstanding balance.
Every EMI reduces the principal amount, which lowers future interest payments.
As a result, the total repayment amount becomes considerably lower.
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Which is Better: Flat or Reducing Interest Rate?
Reducing interest rates is generally considered better than flat interest rates because interest is charged only on the outstanding loan balance, resulting in a lower overall borrowing cost.
Why reducing interest rates is usually preferred:
- Interest is calculated only on the remaining principal amount.
- The interest component decreases with every EMI.
- The total interest payable is generally lower.
- Part-prepayments and foreclosures can lead to greater interest savings.
- The effective borrowing cost is usually more transparent.
In contrast, flat interest rates are calculated on the original loan amount throughout the loan tenure, even though the outstanding principal keeps reducing. This can result in a significantly higher effective interest cost than the advertised rate suggests.
Before taking any loan, borrowers should look beyond the advertised interest rate and evaluate how the interest is calculated, the effective borrowing cost and the total repayment amount to make a well-informed financial decision.
Disclaimer- The rankings and figures in this article have been compiled from multiple verified reports, credible news sources, and public financial data available as of 2026.
All values are approximate and may vary with newer updates, revisions, or changes in official records.
FAQs
A flat interest rate is calculated on the original loan amount throughout the loan tenure, while a decreasing or reducing interest rate is calculated on the outstanding loan balance after each EMI. As the principal decreases, the interest payable under the reducing method also declines.
Reducing interest rates is generally considered better because borrowers pay interest only on the remaining loan balance, resulting in a lower overall borrowing cost than flat interest rates.
For most long-term loans, reducing interest rates is more cost-effective because the interest component decreases as the outstanding principal reduces. Flat rates can result in a higher effective borrowing cost even if the advertised rate appears lower.
A flat interest rate is a method of calculating interest on the entire original loan amount for the whole loan tenure, regardless of how much of the principal has already been repaid.
There is no single conversion formula because the equivalent reducing rate depends on the loan amount, tenure and repayment schedule. Financial calculators typically compare both methods by calculating the total interest payable and effective borrowing cost under each structure.
Reducing interest rates is generally considered beneficial because interest is charged only on the outstanding loan balance, lowering the total interest payable over time. However, the suitability of any loan also depends on factors such as tenure, repayment terms and overall borrowing costs.
