Flat vs reducing interest rate: what is the difference and which costs more?
A flat interest rate charges interest on the original loan amount for the whole term, while a reducing balance rate charges interest only on the outstanding principal. For the same quoted percentage, flat interest costs far more. For example, 12% flat on a ₹1,00,000 one-year loan is roughly 21.5% on a reducing basis.
What is a flat interest rate?
With a flat rate, interest is calculated once on the original principal and spread across the term. If you lend ₹1,00,000 at 12% flat per year for 12 months, interest is ₹1,00,000 × 12% × 1 year = ₹12,000. The total repayable is ₹1,12,000 and the monthly installment is ₹1,12,000 ÷ 12 = ₹9,333.33.
The key point is that the interest does not fall as the borrower repays. In the last month, the borrower owes only about one installment of principal but still pays the same share of interest as in month one.
What is a reducing balance interest rate?
With a reducing balance rate, interest each period is charged only on the principal still outstanding. The same ₹1,00,000 at 12% a year, which is 1% a month, repaid in 12 equal monthly installments gives an installment of about ₹8,884.88.
In month one, interest is 1% of ₹1,00,000 = ₹1,000, and the rest of the installment (₹7,884.88) repays principal. In month two, interest is 1% of the new, lower balance, so more of the installment goes to principal. Over 12 months the total repaid is about ₹1,06,618.55, so total interest is about ₹6,619.
How do the two methods compare side by side?
The table uses the same loan: ₹1,00,000 for 12 months with a quoted rate of 12% a year under each method.
| Point | Flat rate | Reducing balance |
|---|---|---|
| Interest is charged on | Original principal, every month | Outstanding principal only |
| Total interest | ₹12,000 | About ₹6,619 |
| Total repayable | ₹1,12,000 | About ₹1,06,619 |
| Monthly installment | ₹9,333.33 | About ₹8,884.88 |
| Approximate true yearly rate | About 21.5% on a reducing basis | 12% |
| Easy to calculate by hand | Yes | Needs a formula or calculator |
Why does a flat rate cost so much more?
A flat rate keeps charging interest on money the borrower has already returned. By month six, around half the principal is repaid, yet flat interest is still computed as though the full ₹1,00,000 were outstanding.
Here is a quick way to think about it. On average, the borrower holds only about half the loan over the term, because the balance falls steadily to zero. A flat rate charged on the full amount is therefore roughly double the true rate on money actually used. This is why 12% flat is close to 21.5% reducing for a one-year loan.
The same comparison holds for other terms. A 12% flat rate over 24 months works out to roughly 21.6% on a reducing basis, and over 6 months to roughly 20.3%. The exact figure depends on the term and the installment frequency.
Which method do daily and weekly lenders use?
Daily and weekly finance usually quotes a flat charge for the term because it is simple to explain and to collect: one total, split into equal installments. Monthly-interest loans, such as interest-only loans, often charge a percentage on the outstanding principal each month, which behaves like a reducing method.
Consider a ₹10,000 loan repaid over 100 days with a 20% flat charge. The borrower pays ₹2,000 in total, whether they repay on schedule or are one day from finishing. If the same ₹2,000 were charged as interest on the falling balance, a borrower who repays early would pay less. That is the practical difference: flat pricing rewards the lender for the full term, while reducing pricing rewards the borrower for repaying faster.
Both can be used fairly. The problem arises when the borrower believes a "flat 2%" is the same as "2% a month on the balance". Always state the total repayable in rupees, not just the percentage, and be ready to explain the yearly equivalent if the borrower or a regulator asks. For lenders that fall under RBI rules, check the latest circulars on how interest rates and charges must be disclosed.
How do you explain this to a borrower in plain language?
Avoid jargon. Say: "You are borrowing ₹10,000. You will repay ₹120 a day for 100 days, which is ₹12,000 in total. So the extra you pay is ₹2,000." A borrower understands rupees and days far better than rates.
If you offer both options, show them as two printed examples side by side. DailyRupee supports both flat EMI and interest-only loans and shows a live calculator preview before the loan is created, so the borrower can see the installment and total before agreeing.
Frequently asked questions
Is flat or reducing interest better for the borrower?
For the same quoted percentage, a reducing balance rate costs the borrower less because interest falls as principal is repaid. A flat rate costs more in total.
How do I convert a flat rate to a reducing rate?
A rough rule is that a flat rate is close to double on a reducing basis for a typical term. For the exact figure, work out the installment and find the rate that makes the repayments equal to the loan, using a calculator or spreadsheet.
What is the EMI on ₹1,00,000 at 12% flat for one year?
Interest is ₹12,000, total repayable is ₹1,12,000, and the monthly installment is about ₹9,333.33.
Do I have to disclose the effective rate?
Disclosure rules depend on the type of lender. NBFCs and other regulated entities should follow the latest RBI circulars on rate and charge disclosure. Check with a qualified adviser for your case.