Compare the whole cash budget
One option pays the regular EMI and invests the surplus. The other pays the same EMI plus surplus into the loan. Both households must use the same monthly budget, the same comparison date and the same property. Counting property appreciation for only one side would manufacture an advantage.
For a ₹50 lakh loan at 8.5% over 20 years, the EMI is approximately ₹43,391. With another ₹10,000 available monthly, the comparison budget is ₹53,391. In the prepayment route, the loan ends around month 155 under a constant-rate model. Money previously used for EMI then goes into investment; it is not left idle.
At an assumed 10% investment return with month-end deposits, the illustrative end-date investment corpus is about ₹66.47 lakh for prepayment followed by investing, versus ₹75.94 lakh for parallel SIP. That outcome changes when the market-return assumption changes. Neither number is a guaranteed realised wealth outcome.
Subtract debt before naming a winner
During the loan period, investment corpus alone can favour the investing route while ignoring outstanding debt. Net financial wealth is the investment corpus minus remaining loan balance. The calculator displays both paths annually.
What the estimate leaves out
Floating rates, prepayment fees, realised investment tax, home-loan deductions and the personal value of becoming debt-free can change the decision. A higher expected market return is not the same as a known interest saving. Test a low-return path and consider whether the surplus remains available during a loss of income.