Prepay the loan or invest the surplus?

How this calculator thinks about the decision

The question "prepay or invest?" is fundamentally about comparing two interest rates:

• The effective cost of your loan after tax benefits (for a home loan, much lower than the nominal rate; for a car or personal loan, the nominal rate itself).
• The effective return on your investment after tax on gains — equity LTCG is 12.5% with the first ₹1.25 lakh of gains each year exempt; debt is taxed at your slab; PPF is tax-free.

If the effective investment return is higher, investing mathematically wins. If the effective loan cost is higher, prepaying wins.

For home loan borrowers in 30% slab

₹50L outstanding at 8.5% over 20 years, 30% slab, on the old regime: the ₹2 lakh Section 24(b) cap shelters only 64% of your lifetime interest (just 47% in year 1), so the effective rate is 6.79% — not the 5.95% a naive rate × (1 − slab) would give you. Equity at 12% gross → 10.5% after 12.5% LTCG. Investing wins, but by ~0.9%/yr, not 4%.

Same loan on the new regime: Section 24(b) is zero, so the loan costs the full 8.5%. Investing still wins at 12%, but equity now has to clear 9.38% gross just to break even — against 8.33% on the old regime. Below roughly 9%, prepaying wins outright.

For car or personal loan borrowers in 30% slab

Personal loan at 14%: no Section 24(b) at all, so the effective rate is the full 14%. Equity at 12% pre-tax → ~10.5% after LTCG. Prepaying wins comfortably — and it is the guaranteed option, not the risky one. Clear expensive debt before investing a rupee.

The math is only half the story

Even when investing wins mathematically, prepayment has non-financial benefits:

• Psychological peace — being debt-free is its own reward, especially in volatile markets
• Guaranteed return — prepaying gives a certain saving; investments may underperform expectations
• Cash flow improvement — lower EMI frees monthly income for other goals
• Reduced financial vulnerability — less debt means more resilience to income disruptions (job loss, illness)

Many financial planners suggest a hybrid approach: prepay enough to cut your loan tenure to a comfortable level (15 years instead of 25, say), then invest the rest. This balances mathematical advantage with psychological comfort.

When investing definitely doesn't make sense

• If you have credit card debt at 36-42% (always pay this off first)
• If you have personal loan debt above 15% (usually pay this off before investing)
• If you don't have an emergency fund of 6 months' expenses (build that first)
• If you're close to retirement and prioritizing safety

Related calculators & reading

• When prepaying loses to investing
• Prepayment optimizer
• Section 24b & 80C tax benefits
• Prepay: reduce EMI or tenure?