We occasionally misunderstand the true meanings of these two phrases, but you've come to the proper place. We shall describe them in detail here, along with the distinction between a flat interest rate and a declining interest rate. This blog provides actual data to explain why a "10% flat rate" loan might be more expensive than a "15% reducing rate" loan.
What is a flat interest rate?
When a lender charges interest on the full principal amount of a loan, this is known as flat interest. Every time you take out a loan, interest is computed on the entire loan amount, which you must pay back via EMIs. When your outstanding balance decreases, the bank does not lower the interest base.
Flat interest rate formula
Total Interest = Principal (P) × Rate (R) × Tenure in years (T)
Total Repayment = Principal + Total Interest
Flat Rate EMI = Total Repayment ÷ Tenure in months
Let's understand this by one example: you take a personal loan of Rs. 500,000 at a flat interest rate of 10% p.a. for 3 years.
Total Interest = 500,000 × 0.10 × 3 = Rs. 150,000
Total Repayment = 500,000 + 150,000 = Rs. 650,000
Flat Rate EMI = 650,000 ÷ 36 = Rs. 18,056/month
Note that the interest of Rs. 150,000 is charged as if you owed the full Rs. 500,000 for all 3 years even though you've been paying it down every month.
What is a reducing interest rate
It means that you pay interest on the remaining loan balance when you lower the interest rate. Your outstanding principal amount drops as you keep making your EMI payments. With each EMI, the interest amount also decreases because the interest is computed on the remaining principal. This is the reason it's also known as the reducing balance EMI method: over time, your main component increases while your interest component decreases.
Let's understand this by one EMI example:
EMI = [P × r × (1+r)^n] ÷ [(1+r)^n − 1]
Where:
P = Principal amount
r = Monthly interest rate (annual rate ÷ 12)
n = Loan tenure in months
Example: Same loan of Rs. 500,000 at 10% p.a., reducing balance, for 3 years (36 months).
Monthly rate (r) = 10% ÷ 12 = 0.8333%
EMI = Rs. 16,136/month
Total Repayment over 3 years = 16,136 × 36 = Rs. 580,896
Total Interest Payable = 580,896 − 500,000 = Rs. 80,896
Flat and reducing interest rate difference: side-by-side comparison
Same loan amount, same nominal rate (10%), same tenure (3 years), very different outcomes.
Parameter | Flat Interest Rate | Reducing Balance Rate |
|---|---|---|
Interest calculated on | Original principal (constant) | Outstanding principal (declining) |
Monthly EMI | Rs. 18,056 | Rs. 16,136 |
Total Interest Payable | Rs. 150,000 | Rs. 80,896 |
Total Repayment | Rs. 650,000 | Rs. 580,896 |
Interest component over time | Constant | Decreases month on month |
Principal component over time | Constant | Decreases month on month |
At the same nominal rate, the reducing balance method costs you nearly Rs.69,000 less in interest over 3 years on this loan. This is the only biggest reason reducing balance is considered the more equitable, more transparent method and why it's the industry standard approach for most Indian lenders on personal loans, home loans, and automobile loans today.
Why a “lower” flat interest rate can actually be more expensive
Borrowers are caught in this situation. Although the two figures aren't comparable on a like-for-like basis, lenders may promote an alluringly low flat rate because it appears smaller than a decreasing rate. A general rule of thumb: a flat interest rate translates to a meaningfully higher effective interest rate once converted to a comparable reducing balance. often somewhere in the range of 1.7x to 2x the flat rate, depending on the loan tenure (the shorter the tenure, the wider the gap). So a loan advertised at "10% flat" could have an actual interest rate of 17–18% or more on a reducing balance basis. This is why almost every financial regulator and knowledgeable borrower pushes for contrasting loans using the effective interest rate, not the headline flat rate. That's why we should never compare a flat rate quote directly against a reducing rate quote; always convert one to the other first or ask the lender for the reducing equivalent.
Which is better for personal loan: a flat or reducing interest rate
Always remember that for a personal loan a reducing interest rate is more reliable and cheaper as compared to flat interest rate because
You only pay interest on what you actually owe: as your outstanding principal shrinks, so does your interest burden.
Total repayment amount is lower for the same nominal rate and tenure.
It rewards prepayment: Since future interest is computed on the lower balance, your interest savings are immediate and significant if you make a partial payment or foreclose on the loan early. Early repayment may not decrease your interest liability in the same way under a flat-rate loan, and any advantage may be further limited by foreclosure charges.
It's more transparent: the interest cost visibly aligns with what you actually owe at any point in time.
For products like two-wheeler loans, some auto loans, and some small-ticket loans, flat rates are still frequently used. This is mostly due to the ease of high-volume lending, but for personal loans in particular, the majority of respectable lenders and NBFCs currently use reducing balance, which is what borrowers should actively seek out.
Beyond the Interest Rate: What Else Affects Your Borrowing Cost
When comparing personal loan interest rates, don't stop at the interest calculation method. Also factor in:
Processing fees: Typically, an upfront fee of 1% to 3% of the loan amount
Prepayment charges: The interest savings from lowering the sum may be countered by a fee that some lenders impose for early repayment.
Foreclosure charges: an additional fee for completely terminating the loan before its term expires
Effective Annual Interest Rate: the actual cost of the loan once compounding and fees are taken into account
A personal loan calculator that accounts for the reducing balance method, along with these charges, gives you the most accurate picture of loan affordability before you sign.
FAQs
What is a flat interest rate?
Regardless of the amount of principal you have previously repaid, interest is computed on the total original principal for the duration of the loan.
What is a reducing interest rate?
A "reducing" or "diminishing" balance is the result of a method in which interest is only computed on the outstanding (remaining) principal balance. As you repay the loan, the interest amount decreases.
Which interest rate is better for a personal loan?
In general, lowering the balance rate is preferable since it encourages early repayment and reduces the total interest payable for the same nominal rate.
Is a reduced interest rate cheaper than a flat rate?
Indeed, since interest is only assessed on the amount you really owe, lowering your balance results in a far lower total interest payment at the same nominal interest rate.