Understanding Mortgages: Home Loan EMI with Down Payment

What is a mortgage?

A mortgage is a home loan secured by the property you're buying. You put down a percentage upfront (the down payment) and borrow the rest from a bank at an agreed interest rate, then repay in monthly EMIs over a fixed tenure.

Every mortgage calculation starts with one decision: how much are you borrowing vs. how much are you paying from your pocket upfront?

The Mortgage Formula

Two steps:

Step 1 — Compute the loan amount: Loan = Property Value × (1 − Down Payment % / 100)

Step 2 — Apply the EMI formula on that loan: EMI = [P × r × (1+r)^n] / [(1+r)^n − 1]

Where:

P = loan amount from Step 1
r = monthly interest rate (annual rate ÷ 12 ÷ 100)
n = tenure in months

Worked Example

For a ₹80 lakh property with 20% down payment at 8.5% for 20 years:

Down payment: ₹80L × 20% = ₹16L (from your savings)
Loan amount: ₹80L − ₹16L = ₹64L
EMI ≈ ₹55,541/month
Total paid over 20 years: ~₹1.33 Cr
Interest cost: ~₹69.3L

That's 108% of the loan amount paid in interest alone.

How Down Payment Changes Everything

Bumping down payment from 20% to 30% on the same ₹80L property:

Loan drops from ₹64L to ₹56L
EMI drops from ₹55,541 to ₹48,598 (saves ₹6,943/month)
Total interest over 20 years drops by ~₹8.7L

Rule of thumb: every 5% extra down payment saves ~10% on total interest paid.

Common Indian Mortgage Pitfalls

Over-borrowing on a floating rate — rates can rise 1-2% in a cycle, adding ~10-15% to EMI
Ignoring processing fees and stamp duty — these are 4-8% of property value, on top of your down payment
Forgetting GST on under-construction homes — 5% on the builder portion, not present for resale or completed properties
Home insurance and property tax — budgeted separately from EMI, adds ₹3-8k/month typically