Should You Prepay Your Home Loan or Invest? The Honest Maths

You’ve got a ₹20 lakh home loan and, for the first time in years, ₹15,000 of breathing room in your monthly budget. Your parents say crush the loan. Your colleague swears by SIPs. Both of them are partly right, and both are skipping the maths that actually settles it.

The honest answer isn’t a slogan. It’s a comparison of two end states — and a clear-eyed look at the assumptions hiding inside each one.

The two paths

Let’s frame the choice cleanly. You have a ₹20,00,000 loan at 9% over 20 years, and a spare ₹15,000 a month for the next 20 years. You can:

• Path A — Prepay: Throw the ₹15,000 at the loan each month, close it early, then redirect the freed-up cash (the EMI you no longer pay) into investments for whatever time remains.
• Path B — Invest: Keep paying your normal EMI, and put the full ₹15,000 into the market every month for the whole 20 years.

Whichever leaves you with more net worth at the end of 20 years wins. Note that prepaying is itself a kind of investment — see how prepayment reduces EMI — because every rupee you prepay “earns” you a guaranteed saving equal to your loan rate.

The worked comparison

Assume the market delivers an expected 12% pre-tax return over the horizon. Here’s roughly where each path lands after 20 years:

Path	What you do with ₹15,000/month	Approx. net worth after 20 years
Invest (Path B)	Invest it all, every month, for 20 years	~₹1.48 crore
Prepay (Path A)	Prepay the loan, then invest the freed-up EMI	~₹1.26 crore
Edge to investing	—	~₹22 lakh

At a 12% expected return, investing the surplus comes out ahead — by roughly ₹22 lakh. The reason is intuitive: prepaying “earns” you a guaranteed 9% (your loan rate), while the market is expected to earn 12%. That 3-percentage-point gap, compounded over two decades on a growing pile of money, is worth a lot.

Find your break-even

The result flips entirely depending on the return you assume. The pivotal figure is the break-even return — and it sits right around your loan rate of 9%.

• If you genuinely expect the market to return more than ~9% over your horizon, investing wins on the maths.
• If you expect less than ~9%, prepaying wins.
• At exactly 9%, it’s a wash — because prepaying is mathematically identical to earning a guaranteed, tax-free 9% on your money.

That last point is the one most people miss. Prepaying a 9% loan is a risk-free 9% return. To beat it, an investment doesn’t just need to average more than 9% — it needs to clear 9% reliably enough that you’re comfortable taking the risk. You can test different rates and horizons yourself in the loan vs invest calculator.

The caveats that change everything

Those numbers are clean. Real life is not. Here are the three honest adjustments — and notice they don’t all point the same way.

1. Taxes on gains (usually favours prepaying)

The ~₹1.48 crore from investing is a pre-tax figure. When you eventually sell, capital gains tax takes a bite, shrinking your real advantage. The 9% you save by prepaying, on the other hand, is entirely tax-free — there’s no tax on money you didn’t spend on interest. Factor taxes in and investing’s lead narrows.

2. The home-loan interest deduction (favours investing)

If you claim a tax deduction on your home-loan interest, your effective loan rate is lower than the headline 9%. A loan that genuinely costs you, say, 7% after the deduction is a much easier hurdle for the market to clear — which tilts the scales back toward investing. The maths above ignores this benefit entirely.

3. Market volatility (prepaying is certain, investing is not)

This is the big one, and no spreadsheet captures it honestly. The 12% return is an expectation, not a promise. Markets fall. They can stay flat for years. The ~₹1.48 crore could turn out to be ₹1.7 crore or ₹1.1 crore — you simply won’t know until you get there. Prepaying delivers exactly the saving it promises, on schedule, with zero drama. For some people, sleeping soundly with no loan is worth giving up a few lakh of expected upside.

So what should you actually do?

There’s no universal answer, but a few sensible principles:

• If your loan rate is high (closer to or above what you realistically expect from the market), prepay. The certainty is almost free. The same logic that makes a longer tenure expensive — explored in The Real Cost of a Longer Loan Tenure — makes early prepayment powerful.
• If your loan rate is low (especially after the tax deduction) and you have the temperament for market swings, investing is likely to win over a long horizon.
• You don’t have to pick one. Many people split the surplus — part to prepayment for guaranteed progress, part to investing for growth. It’s rarely the mathematically optimal choice, but it’s often the most liveable one. If you do prepay, doing it early in the tenure saves the most, as we cover in Part-Payment Strategy: When It Saves Most.

The takeaway

On paper, with a 9% loan and a 12% expected return, investing your ₹15,000 surplus beats prepaying by roughly ₹22 lakh over 20 years. But “expected” is doing heavy lifting in that sentence. Prepaying hands you a guaranteed, tax-free return equal to your loan rate — and the moment your expected market return dips below that rate, prepaying wins outright.

These figures are illustrative estimates that ignore taxes, the home-loan interest deduction, and market risk — all of which matter to your real outcome. Run your own numbers through the loan vs invest calculator, then decide whether the extra expected rupees are worth the uncertainty. There’s no wrong answer here — only an informed one.