The advice on this question is unusually bad. One camp says always prepay, because debt is risk. The other says always invest, because equities beat 8%. Both are asserting a conclusion that depends entirely on a number neither of them names.
So we computed it.
What we modelled
A ₹50 lakh home loan over 20 years at 8.5%, giving an EMI of ₹43,391. Then an extra ₹10,000 a month, deployed two ways:
Path A — prepay. Put the ₹10,000 into the loan every month. It clears in 155 months instead of 241, saving ₹21.79 lakh of interest. From month 156, the entire ₹53,391 that was going to the loan gets invested instead, for the remaining 86 months.
Path B — invest. Pay the normal EMI for the full 241 months and invest the ₹10,000 every month throughout.
Both paths are compared at the same moment — month 241, when the untouched loan would have ended. This matters, and it is where most comparisons go wrong: they measure the interest saved against an investment pot without accounting for the fact that a paid-off loan frees up the entire EMI.
The result
| Return assumed | Path A: prepay, then invest | Path B: invest throughout | Winner |
|---|---|---|---|
| 8% | ₹62.1 lakh | ₹59.8 lakh | Prepay, by ₹2.4 lakh |
| 10% | ₹67.3 lakh | ₹77.3 lakh | Invest, by ₹10.0 lakh |
| 12% | ₹73.0 lakh | ₹101.0 lakh | Invest, by ₹28.0 lakh |
| 14% | ₹79.2 lakh | ₹133.3 lakh | Invest, by ₹54.0 lakh |
Prepaying wins at 8%. Investing wins at 10%. The crossover is somewhere between — and when we solved for it precisely, it landed at 8.44%, against a loan rate of 8.5%.
The finding: we repeated this at loan rates of 7.5%, 8%, 8.5%, 9%, 9.5% and 10%. The crossover return came out at 7.57%, 7.92%, 8.44%, 8.96%, 9.46% and 9.96% respectively — within 0.1 percentage points of the loan rate in every case. The decision is not really about your loan term, your EMI, or how much you can spare. It is one question: can you reliably earn more than your loan rate, after tax?
Why it lands there
Prepaying is a guaranteed, risk-free return exactly equal to your loan rate. Every rupee you put in saves you that rate, compounded, for the remaining term. There is no other risk-free instrument that pays what your own mortgage does.
So the comparison was never really "loan versus market". It is "a guaranteed 8.5% versus an uncertain something else". Once you see it that way, the crossover sitting at the loan rate is not a surprising empirical result — it is arithmetic that the modelling confirms rather than discovers.
The word doing the work is "reliably"
The table above assumes you actually achieve the stated return, every year, without interruption. Reality intrudes in four ways.
Tax. Equity gains are taxed on realisation. A 12% gross return is not 12% in your hand. Prepayment returns are untaxed — you are not earning income, you are avoiding an expense, and nobody taxes an avoided expense. Comparing a pre-tax investment return against a loan rate quietly overstates the investment case.
Sequence. The model assumes a smooth 12%. Markets deliver it as +30%, −18%, +22%, and your own behaviour during the −18% year is the variable nobody models honestly.
Discipline. Path B requires investing ₹10,000 every month for twenty years without diverting it. Prepayment is structurally enforced; a SIP is not. The realistic comparison for many people is not prepay-versus-invest but prepay-versus-intending-to-invest.
Old-regime tax relief. If you are on India's old regime and claiming Section 24(b) interest deduction, your effective loan rate is lower than the headline — which pushes the crossover down and favours investing. On the new regime, which is now the default, there is no such deduction and the headline rate is the real rate.
What actually decides it for most people
- Clear the expensive debt first, always. A credit card at 36–42% is not a close call against any investment. Neither is a personal loan at 14–18%. This entire analysis only applies to cheap, long-dated, secured debt.
- Build the emergency fund before either. Prepaying is irreversible — money in the loan is not available when the boiler fails. Six months of expenses in cash comes before any optimisation.
- Take the employer match first. A matched retirement contribution is an instant 50–100% return. Nothing on this page competes with that.
- If the crossover is close, prepay. When the expected return is within a point or two of your loan rate, you are taking equity risk for a marginal gain. Certainty is worth something, and the model does not price it.
- Reduce the EMI or the tenure? On prepayment most banks default to shortening the tenure, which saves far more interest. Reducing the EMI helps monthly cash flow instead. Shortening is usually the better financial answer; ask explicitly, because you will not be offered the choice.
The honest summary
If your loan is at 8.5% and you genuinely expect 12% from equities over twenty years, investing wins by around ₹28 lakh on these numbers, and that is a large enough margin to survive some slippage. If you expect 9%, the margin is thin enough that certainty is arguably worth more than the difference.
And if you are not going to invest the money consistently, prepay. A guaranteed 8.5% beats an aspirational 12% that does not happen.