Flat Interest Rate EMI — From Intuition to Precision
Imagine you borrow ₹1,00,000 from a bank for 1 year. The bank says: "We charge 12% interest per year, flat." What does "flat" mean here?
The intuition: The bank calculates the total interest on the entire original loan amount for the full loan tenure, regardless of how much you've already repaid. You pay interest on the full ₹1,00,000 for the whole year — even though you're paying back the principal bit by bit each month.
Step-by-step breakdown
Let’s take a concrete example:
- Loan amount (P): ₹1,00,000
- Annual flat interest rate (R): 12%
- Tenure (N): 1 year (12 months)
Step 1: Total interest for the year
Interest = Principal × Rate × Time
= ₹1,00,000 × (12/100) × 1 = ₹12,000
Step 2: Total amount to repay
Principal + Interest = ₹1,00,000 + ₹12,000 = ₹1,12,000
Step 3: Monthly EMI
EMI = Total amount ÷ Number of months
= ₹1,12,000 ÷ 12 = ₹9,333.33 per month
Every month you pay ₹9,333.33. The interest portion in each EMI is not decreasing — it's a fixed ₹1,000 per month (₹12,000 ÷ 12). The principal repaid each month is also fixed: ₹8,333.33.
The precise formula
EMIflat=NP+(P×R×N)
Where:
- P = original loan principal
- R = annual flat interest rate (as a decimal, e.g., 0.12 for 12%)
- N = loan tenure in months (or years, as long as consistent)
Alternatively, in a cleaner form:
EMIflat=NP+12P×R
The first term is the fixed principal repayment per month. The second term is the fixed monthly interest.
Why "flat" is important — and a warning
A flat interest rate looks lower than the equivalent reducing-balance rate, but it's actually more expensive.
In our example, 12% flat is equivalent to about 21.5% reducing-balance interest — nearly double. …