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Flat vs Reducing Interest Rate: Why a "Low" Flat Rate Costs More
If a lender quotes you a "flat" interest rate, treat it with suspicion — it almost always costs far more than the same number on a reducing-balance basis. A flat rate charges interest on the full loan for the entire tenure, even though you're steadily paying it off. A reducing-balance rate charges interest only on what you still owe. The practical result: a 10% flat rate is roughly the same as an 18% reducing rate. Always compare loans on the reducing-balance (effective) rate, which is what banks use.
The core difference
Every loan repayment is part interest, part principal. What differs is how the interest is worked out:
- Reducing balance — interest each month is charged only on the outstanding balance. As you repay, the balance falls, so the interest portion shrinks and more of your EMI goes to principal. This is how bank loans work.
- Flat rate — interest is calculated once, on the entire original loan, for the whole tenure, and simply divided across the EMIs. You keep paying interest on money you've already repaid.
A worked example
Take a ₹5 lakh loan for 3 years. At a 10% flat rate, the interest is ₹5,00,000 × 10% × 3 = ₹1,50,000, making the EMI about ₹18,056. At a 10% reducing rate, the EMI is about ₹16,134 and the total interest only ₹80,878. Same headline number, but the flat version costs you nearly ₹70,000 more. Run the flat rate through an effective-rate calculation and that "10%" turns out to be about 17.9% reducing — almost double.
The rough 1.8x rule
There's no single conversion factor, but for typical tenures a flat rate is around 1.7 to 1.9 times the equivalent reducing rate. A quick mental check: whatever flat rate you're quoted, nearly double it to picture the real cost. The longer the tenure, the wider the gap — because more of the loan is repaid while flat interest keeps charging on the full amount.
Where you'll meet flat rates
Flat quotes turn up most in two-wheeler dealer finance, consumer-durable EMIs and some informal lending. Banks' home, car and personal loans use reducing balance. If you're ever given a flat rate, ask for the reducing-balance (or "effective" / APR) figure so you can compare like with like.