You have a ₹50,000 monthly surplus beyond your regular expenses and EMI. Two options stare at you: drop it on the home loan principal, or park it in a SIP.
Both feel prudent. Both are better than spending it. But they have very different outcomes over a 10-15 year horizon — and the decision turns on a few numbers that most people get wrong.
The basic math first
A home loan at 8.75% is costing you 8.75% on every rupee of outstanding principal — certain, predictable, risk-free "return" if you prepay.
A diversified equity SIP has historically delivered 11-13% CAGR over 10+ year horizons in India. But equity returns are uncertain, volatile, and not guaranteed.
The naive answer is: invest, because 12% > 8.75%. The real answer is more nuanced.
Three factors that change the calculation
1. Your tax regime
Under the old tax regime, home loan interest (up to ₹2 lakh/year) is deductible under Section 24(b). If you're in the 30% tax bracket, ₹2 lakh of deductible interest saves you ₹62,400 in taxes. This effectively reduces your true borrowing cost.
Example: 8.75% nominal rate, 30% bracket, old regime → effective rate ~7.6%.
Under the new tax regime (default since FY 2024-25), this deduction is unavailable. Your effective rate equals your nominal rate: 8.75%.
The wider the gap between your post-tax loan rate and expected investment return, the more investing wins.
2. Your investment discipline
If the surplus isn't invested — if it slowly disappears into lifestyle inflation, discretionary spending, or idle cash — then prepayment is better by default. You can't lose money to discipline failure when you've already sent it to the lender.
Be honest with yourself about this. A systematic prepayment is worth more than a theoretical SIP that never actually gets set up.
3. Your stage in the loan
Interest front-loading is real. In a 20-year home loan, your EMIs in the first 5-7 years are predominantly interest, not principal. Every rupee of prepayment in these early years saves the most total interest. The later in the loan you are, the less each prepayment dollar saves.
Info
If you are in the first 5 years of a home loan, the compounding math of early prepayment is particularly powerful. Eliminating ₹10 lakh of principal in year 3 might save ₹20-22 lakh in total interest. That's a 100-120% guaranteed return — tough for equity to match on a risk-adjusted basis.
Run your actual numbers
The correct answer for you depends on your loan balance, remaining tenure, interest rate, and expected investment return. Use the calculator below to compare:
What the numbers usually show
For a typical case — ₹50,000 monthly surplus, ₹60 lakh loan outstanding at 8.75%, 15 years remaining, 12% expected SIP return:
- Investing the surplus (SIP): After 15 years, SIP corpus of approximately ₹2.5 Cr. Loan repaid at end of term normally.
- Prepaying the loan: Loan closes in ~9 years instead of 15. After loan closes, the full ₹50,000 goes into SIP for 6 years. Total corpus after 15 years: approximately ₹2.0-2.2 Cr.
In this scenario, investing wins by roughly ₹30-50 lakh — before accounting for the tax benefit on home loan interest.
But change the assumptions: raise the loan rate to 9.5%, shorten the loan tenure to 7 years, or assume 10% SIP return instead of 12%, and prepayment starts to look better.
Warning
The spread between your loan rate and expected equity return is the key variable. Under 1.5 percentage points of spread, the choice is basically a coin flip adjusted for your personal risk tolerance. Over 3 percentage points of spread, invest — but confirm you'll actually do it.
The hybrid approach
For most families, a split is the pragmatic answer:
- Invest 70% of surplus in equity SIP (captures compounding)
- Prepay 30% of surplus on loan principal (reduces interest burden and gives psychological benefit)
This hedge means you don't fully lose if equity underperforms, and you don't sacrifice all the compounding advantage if equity outperforms. The psychological benefit of seeing the loan balance shrink alongside an investment portfolio also matters — financial decisions you stick with are better than theoretically optimal ones you abandon.
A note on liquidity
This is the strongest argument for investing over prepaying: liquidity.
Money prepaid into a home loan is gone. You cannot easily get it back. In a financial emergency, you can't call your lender and say "I prepaid ₹8 lakh last year, please return it." You'd need to take a top-up loan or personal loan — at higher rates.
Money in a mutual fund is accessible within 2-3 business days. That optionality has real value, especially if you're in a volatile career or business phase.
If your emergency fund is thin (under 3 months), build that first before deciding between prepayment and SIP.
SIP Calculator
Will a steady SIP actually grow into the corpus you need? See the final number, what drives it, and whether your plan is aggressive, balanced, or lagging.
Try with your numbersThe final answer
- Invest if: Your post-tax loan rate is below 9%, you have 10+ years remaining, your emergency fund is solid, and you will actually invest the surplus
- Prepay if: Your loan rate is above 9.5%, you are within 7 years of loan closure, or you know yourself well enough to know the surplus will leak otherwise
- Split if: You are uncertain about discipline, want psychological benefit of loan reduction, or your margin between rates is thin
Either way: don't let the decision take longer than a month. The compounding clock runs regardless.