Flat Rate or Reducing Balance: The Difference That Changes What You Repay

A flat rate charges interest on the original loan amount for the whole tenor, however much you have already repaid. A reducing balance rate charges it only on what you still owe, so every instalment shrinks the base. The two are not variants of one thing: on Rs 1,00,000 over 24 months at 10 percent, flat produces about Rs 20,000 of interest and reducing about Rs 10,750. A flat 10 percent is worth roughly 18 percent on a reducing basis, which is why the two numbers must never be compared as if they were the same quote.

What is the difference, mechanically?

Flat interest is computed once, at the start: principal x rate x years, and nothing you do later changes the base. The instalment is then simply the total divided by the number of months.

Reducing balance interest is computed on the amount outstanding each period, so month one carries the most interest and by the last month almost the whole instalment is principal. Over an amortising loan the average amount outstanding is roughly half the original, which is the intuition behind the whole comparison: charging a rate on the full principal throughout costs about twice as much as charging it on the balance.

How different is the money, on the same headline rate?

Take Rs 1,00,000 over 24 months at 10 percent a year both ways.

• Flat. Interest 1,00,000 x 0.10 x 2 = Rs 20,000, total Rs 1,20,000, instalment 1,20,000 divided by 24 = Rs 5,000 a month.
• Reducing balance. At 10 percent on the outstanding amount the level instalment is about Rs 4,615 a month, about Rs 1,10,750 over 24 months, so about Rs 10,750 of interest.

The difference is about Rs 9,250 on a one-lakh loan, and the flat interest bill is about 1.86 times the reducing one. The headline rate was identical; only the basis changed.

A shorter case: Rs 50,000 over 12 months at 12 percent. Flat interest is 50,000 x 0.12 = Rs 6,000, a total of Rs 56,000 and an instalment of about Rs 4,667. On a reducing basis at the same 12 percent the instalment is about Rs 4,442, a total of about Rs 53,309 and interest of about Rs 3,309 — so the flat version costs about Rs 2,691 more for the same money over the same period.

What reducing rate is a flat rate really worth?

This conversion turns an incomparable quote into a comparable one. Solve for the reducing rate that produces the same instalment:

• Flat 10 percent over 24 months gives an instalment of Rs 5,000, matching a reducing rate of about 18.2 percent a year.
• Flat 12 percent over 12 months gives about Rs 4,667, matching a reducing rate of about 21.5 percent a year.

As a working rule, an instalment loan quoted flat is worth somewhere around 1.7 to 1.9 times that rate on a reducing basis, the multiple depending on the tenor. Use it to spot when a quote deserves a proper calculation. You can run both bases on your own principal, rate and tenor in the (Fast Paisa Loan): App SIM app, an independent, unofficial simulation and calculator rather than a lender.

Why does it not matter on a 30-day single-payment loan?

Because there is nothing for the balance to reduce. If the loan is disbursed and repaid once, in full, at the end, the amount outstanding is the full principal for every day of the tenor on either basis. Flat and reducing give the same answer when there is only one repayment. On a one-payment short-term loan, then, the things that move the total are the daily rate, the day count and the charges. The flat-versus-reducing question becomes real the moment the loan is repaid in instalments.

How do you tell which basis an offer is using?

• Check the total interest against principal x rate x years. An exact match means the quote is flat.
• Ask for the amortisation schedule. Under reducing balance the interest portion falls every month; under flat it is identical in every row, or not shown at all.
• Read the wording. Interest on the sanctioned amount, or a monthly charge in rupees that never changes, points to a flat calculation.
• Compare the stated APR with the stated rate. An APR close to twice the headline on an instalment loan means the headline is almost certainly flat.

Lenders in India are expected to give a retail borrower a written key facts summary stating the all-inclusive annualised cost, which is what makes two differently quoted offers comparable at all. Those requirements are published by the Reserve Bank of India on the official RBI website, rbi.org.in.

Does prepayment help under a flat rate?

Much less than under reducing balance, and sometimes not at all. Under a flat contract the interest was computed on day one on the full principal, so clearing the balance halfway through does not automatically remove the interest attached to the second half. Some lenders rebate part of it, some do not, and some add a foreclosure charge. Under reducing balance the benefit is automatic. If you expect to repay early, settle that in writing before you sign.

Frequently asked questions

Is a flat rate always worse than a reducing one?

Not automatically, because the rate matters as well as the basis. A flat 6 percent can beat a reducing 18 percent. Convert both to one basis, or compare the all-in APR, and only then decide.

Why do lenders quote flat rates at all?

The arithmetic is simpler and the number is smaller. Neither is improper as long as the basis is stated and the APR is disclosed. The problem is a flat rate shown beside a reducing one as though they were comparable.

Does the processing fee change with the basis?

No. The fee and the GST on it are charged on the sanctioned amount however interest is calculated, so they sit on top of either figure.

Can an app tell me which basis my lender used?

No. An independent calculator can show what each basis would cost on figures you type in, but only the lender can confirm its own terms. Never enter an Aadhaar number, a PAN, a bank account number, a password or an OTP into any third-party app or website.

Treat the basis as part of the price rather than a technicality: ask which amount interest is charged on, and convert a flat quote to its reducing equivalent before comparing it with anything. To run both calculations on your own numbers, the independent, unofficial app on Google Play works with no account and no login. It is not an official representative of Fast Paise and is not affiliated with, endorsed by, or connected to Fast Paise, and it does not represent the Reserve Bank of India or any other government body. It does not offer loans and cannot be used to apply for a loan; it does not process applications, disburse funds, check application status, or access any account. All figures are estimates for planning only; always confirm the actual terms with Fast Paise directly.