Home loan EMI: how it is calculated, how much is interest, and whether to prepay

For informational purposes only. Home loan interest rates vary by lender and borrower profile. Tax rules on home loan deductions apply under the old tax regime only. Verify current rates and rules before acting.

A home loan is the largest financial commitment most salaried employees make. The EMI feels manageable at the time of purchase — but the total interest paid over 20 years is often more than the loan itself. Understanding the math of how an EMI is structured, how much of it goes to interest versus principal in each phase, and whether prepayment actually saves money is worth knowing before you sign.

How home loan EMI is calculated

The EMI (Equated Monthly Instalment) is a fixed monthly payment calculated so that you pay off the full loan in exactly N months at interest rate r.

Formula:

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EMI = P × r × (1+r)^N / ((1+r)^N − 1)

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Where:

• P = principal loan amount
• r = monthly interest rate = annual rate / 12
• N = total number of months

Example: ₹50 lakh loan, 8.5% per annum, 20-year tenure.

• r = 8.5% / 12 = 0.708% per month = 0.00708
• N = 20 × 12 = 240 months
• EMI = ₹50,00,000 × 0.00708 × (1.00708)^240 / ((1.00708)^240 − 1) = ₹43,391/month

Total paid over 20 years: ₹43,391 × 240 = ₹1,04,13,840

Total interest paid: ₹1,04,13,840 − ₹50,00,000 = ₹54,13,840

You borrow ₹50 lakh and pay back ₹1.04 crore. The extra ₹54 lakh is purely interest.

How the interest/principal split changes over time

EMI amount is fixed. But the split between interest and principal changes every month — dramatically.

In the first month: most of the EMI is interest (8.5% on the full ₹50 lakh). In later months, the outstanding principal is smaller, so the interest portion shrinks and more of the EMI goes toward principal.

Year-by-year breakdown for the ₹50L, 8.5%, 20-year example:

Approximate figures. Exact amounts depend on amortisation schedule.

In Year 1, approximately 84% of your EMI is interest. By Year 20, most of it is principal. This is why early prepayment saves so much — in the early years, almost every rupee of EMI is going to interest, not reducing your debt.

The total interest at different loan tenures

At ₹50 lakh, 8.5%:

A 30-year tenure reduces the EMI by ₹4,945/month compared to 20 years — but costs an additional ₹34.3 lakh in total interest.

Should you prepay? The math of partial prepayment

The prepayment effect: Any lump sum paid toward the principal reduces the outstanding balance, which reduces future interest on that balance.

Example: You are in Year 3 of the ₹50 lakh, 8.5%, 20-year loan. Outstanding balance: approximately ₹48.5 lakh. You make a ₹5 lakh prepayment.

Without prepayment: 17 years remaining, total future interest ≈ ₹43 lakh.

After ₹5L prepayment: outstanding ₹43.5 lakh, same EMI. Loan clears approximately 2.5 years earlier. Total interest saved: approximately ₹6–7 lakh.

The prepayment timing principle: Prepayment in the early years of the loan saves significantly more than the same prepayment in later years. In Year 3, a ₹5 lakh prepayment saves ₹6–7 lakh in future interest. The same ₹5 lakh prepayment in Year 15 saves much less — because the outstanding principal is smaller and the remaining tenure is shorter.

Prepay vs invest: the comparison

Your home loan rate is 8.5%. If you prepay ₹5 lakh, you effectively "earn" 8.5% on that ₹5 lakh (the interest you avoid paying). This is a guaranteed, risk-free return.

If instead you invest the ₹5 lakh in equity mutual funds expecting 12% CAGR (illustration only, not guaranteed), the expected return is higher — but not guaranteed. The 8.5% loan saving is certain; the 12% equity return is not.

General guidance:

• If your loan rate is above 9%: prepayment is hard to beat on a risk-adjusted basis
• If your loan rate is 8–9%: depends on your risk comfort and alternative investment returns
• If your loan rate is below 8%: equity investments historically outperform the loan rate over long periods

◇ Quick check: Look at your loan statement for the current outstanding principal. Calculate 8.5% of that number — that is approximately what you are paying in interest this year. Ask yourself: is there an equivalent risk-free investment earning more? If not, prepayment is often the better use of surplus cash.

Home loan tax deductions (old regime only)

Section 24 — Interest on home loan:

Up to ₹2,00,000 per year of home loan interest is deductible for a self-occupied property under the old tax regime. For a let-out property, there is no ceiling — all interest is deductible (though setoff against other income is limited to ₹2L, with the remainder carried forward).

Section 80C — Principal repayment:

The principal portion of your EMI qualifies for 80C deduction (combined with other 80C investments, up to ₹1.5L total).

None of these deductions are available under the new tax regime. If you are on the new regime, the home loan provides no tax benefit beyond shelter.

At a ₹50L loan at 8.5%, the interest in Year 1 is approximately ₹4.17 lakh. The maximum deductible is ₹2L. At 30% slab, this saves ₹60,000 in tax — a meaningful amount for old-regime taxpayers with large loans.

⚠ Common mistake: Choosing the old regime solely because of a home loan interest deduction, without calculating whether the total old-regime deductions actually reduce your tax below the new regime. Many salaried employees with ₹2L home loan interest + ₹1.5L 80C + ₹25K 80D = ₹3.75L total deductions find the old regime is still better — but some do not. Always calculate both.

Bottom line

• EMI = P × r × (1+r)^N / ((1+r)^N − 1). At ₹50L, 8.5%, 20 years: ₹43,391/month; total interest paid: ₹54 lakh
• In the first years, the majority of your EMI is interest — early prepayment saves far more than late prepayment
• A ₹5 lakh prepayment in Year 3 saves approximately ₹6–7 lakh in future interest on a ₹50L, 8.5% loan
• Prepay vs invest: loan at 8.5% is a guaranteed return — compare against your best risk-free alternative
• Home loan interest deduction (₹2L/year, Section 24) and principal repayment (80C) are available only under the old tax regime

Frequently asked questions

Q: I have a floating rate home loan. What happens if rates rise?

A: Most floating rate home loan lenders extend the tenure (keep EMI same, add months) rather than increase the EMI, unless the EMI no longer covers even the interest. You can track your outstanding loan balance — if it is increasing despite regular EMI payments, your rate has risen past the point where your EMI covers interest.

Q: Is there a penalty for prepaying a floating rate home loan?

A: No. RBI regulations prohibit prepayment penalties on floating rate home loans from banks and NBFCs regulated by RBI. Fixed rate loans may have a penalty (typically 2–4% of the prepaid amount). Check your loan agreement.

Q: My property is jointly held with my spouse. Can we each claim ₹2L interest deduction?

A: Yes, if both are co-borrowers on the loan and co-owners of the property. Each co-borrower can independently claim up to ₹2L of interest deduction in their own ITR (old regime), subject to their share of ownership and the total interest paid.

Q: How do I find my amortisation schedule?

A: Log in to your home loan account online (net banking or the lender's app). Most lenders show the amortisation schedule — month by month principal and interest breakdown — in the loan statement section. You can also request it from your bank branch.

Sources: Home loan deductions, Income Tax Department · RBI guidelines on home loans

Last verified: June 2026. Home loan interest rates are floating and change with repo rate. Tax deduction rules are as per Finance Act 2025 for FY 2025-26.