Loan amortization:
see how each EMI splits into interest and principal

What loan amortization means

Amortization is the process of paying off a loan in equal instalments in which each payment covers the interest for the month and repays part of the principal. An amortization schedule is the table that shows that split for every payment, from the first to the last.

The payment stays the same, but its two parts change. Interest is charged on what you still owe, so it is highest on day one and shrinks as the balance falls. Principal is whatever is left of the instalment after interest, so it grows every month.

Think of it as a running account of the loan. Each row opens with a balance, charges interest, takes a payment, and closes with a smaller balance. Nothing else happens, which is why a spreadsheet with four columns can reproduce a bank schedule almost exactly.

Seeing the schedule matters because it answers questions the EMI alone cannot: how much do I still owe after two years, how much interest will I pay this financial year, and what do I save if I prepay now?

How to build a schedule, one row at a time

You need the EMI first, from the standard reducing-balance formula. After that, every row follows the same three steps.

Worked example: ₹7,50,000 at 9% for 5 years

Rows 2 and 3 repeat the same move. The balance after month 1 is ₹7,40,056, so month 2 interest is 7,40,056 × 0.0075 = ₹5,550, which leaves ₹10,018 for principal. In these early rows the interest part shrinks, and the principal part grows, by about ₹75 a month.

Between month 1 and month 60 the interest part falls from ₹5,625 to ₹116, while the principal part rises from ₹9,944 to ₹15,453. The EMI never moved.

The year-by-year picture

The yearly view is the one most people need for planning. In year 1 about 33% of what you pay is interest; by year 5 it is about 5%. At the halfway point of 30 months you have repaid only about 44% of the principal: the balance is still about ₹4.17 lakh, or 56% of the original loan.

This front-loading is why prepaying early is powerful and why foreclosing late saves little. By year 4 the balance is ₹1.78 lakh and little interest is left to avoid.

How tenure changes the schedule

The EMI falls by about ₹8,300 when you move from 36 to 60 months, but total interest rises by about ₹75,500. Stretching the loan makes each payment lighter and the schedule longer, with a larger share of every early payment going to interest.

Long loans show the effect more sharply. On a 20-year loan at 9%, interest is larger than principal in each EMI for the first 148 months, which is more than 12 years, before the two lines cross. Borrowers who look only at the EMI rarely realise how slowly principal falls at first.

What to do with a schedule

A schedule is a working document, not a printout to file away. Once you have one, a handful of practical questions become quick to answer.

• Find your outstanding balance at any date before you prepay or take a top-up.
• Work out the interest paid in a financial year, which some lenders also give in an annual statement.
• Compare two loans honestly: put both schedules next to each other and look at total interest, not just the EMI.
• Test a prepayment by subtracting it from a row and recomputing the rows below.

Here is a prepayment test on the example loan. After 24 payments the balance is ₹4,89,588. Pay ₹1,00,000 extra and it drops to ₹3,89,588. If the EMI stays at ₹15,569, the schedule ends after 28 more payments instead of 36, and the interest still to be paid falls from about ₹70,888 to about ₹43,516, a saving of about ₹27,372.

That test is only a few lines once you have the table, and it shows why people who understand their schedule ask smarter questions of the lender: does the extra go to principal immediately, and does the tenure or the EMI change?

For the full home-loan picture with a longer tenure, read the home loan EMI guide. For the EMI formula itself and how it moves with rate and tenure, see the mortgage payment guide.

Mistakes people make with amortization

• Using the annual rate in each monthly row instead of dividing it by 12.
• Starting the schedule with the property price rather than the amount borrowed.
• Expecting the lender's schedule to match yours to the rupee. Day-count conventions, rounding and first-instalment dates differ.
• Assuming a floating-rate loan keeps one schedule. A rate change recalculates the EMI or the tenure, so the table must be rebuilt.
• Forgetting fees. Processing fees and insurance are usually outside the schedule but still part of what the loan costs you.

A rate change is a good case to rehearse. Suppose the rate on a floating loan moves from 9% to 10% after 24 payments, with ₹4,89,588 outstanding and 36 months left. Rebuilding the schedule from that point gives a new EMI of about ₹15,798, which is ₹229 more than before. Alternatively, the lender may keep the EMI and extend the tenure, so ask which one applies.

Keep the sanctioned schedule from your lender and compare it with your own once. If the two disagree by more than a few rupees a month, ask why.