Pay off your mortgage or invest the extra money?

Overpaying a mortgage reduces debt and interest. Investing keeps more money in a portfolio whose returns are uncertain. A useful comparison gives both choices the same monthly budget and follows the money after either loan is paid off.

An example with €300 a month to allocate

The example loan has €200,000 outstanding, 25 years left and a fixed 4% nominal annual interest rate. Its calculated payment is €1,055.68 a month. Adding €300 gives both paths a monthly commitment of €1,355.68.

The overpayment path sends the whole budget to the mortgage until it clears, in 17 years. It then invests that same monthly budget. The investing path pays the scheduled mortgage amount and invests the €300 from the beginning. Any final partial loan payment also releases the unused cash for investing.

With a constant 5% annual investment return after fees and ongoing taxes, plus a separate hypothetical 25% tax on positive gains when sold at year 25, investing ends about €1,456 ahead. These percentages are illustrative inputs, not a claim about the tax or returns you will face.

The small difference is worth testing. At a 3% investment return, the same model favors overpaying by €21,239. At 7%, it favors investing by €35,706. Changing the return assumption changes the result without changing the mortgage.

What the comparison measures

The regular payment amortizes the entered loan balance over its remaining term. Mortgage interest is charged monthly using the nominal annual rate divided by twelve. The same regular payment plus the extra money is allocated under both choices.

Investments earn an effective monthly equivalent of the annual investment-return assumption, with new contributions added at the month-end. At each displayed date, tax is applied to positive portfolio gains as if the investments were sold. Contributions are not taxed again, losses do not generate a refund, and no allowances are modeled.

The comparison is after-tax investments minus outstanding mortgage debt. The same house is held under both paths, so its value cancels out. A negative figure early in the table is not the household’s total net worth: the home and other assets are omitted.

All figures are nominal. Both choices use the same fixed cash budget, so an inflation adjustment would rescale their difference at a given date. It would not introduce a new source of money.

Check the loan before assuming overpayments are free

Your contract may limit additional payments, charge for early repayment or reset its interest rate before the full loan term ends. This illustration includes none of those features. Check the actual contract rather than entering today’s fixed rate for decades if it will change sooner.

For example, the US

Consumer Financial Protection Bureau explains

that prepayment penalties depend on loan terms and mortgage type. That is US guidance, not a statement of rules for other countries. Local tax deductions and lender conditions need their own review.

Read liquidity and risk alongside the final difference

Money paid into a mortgage may be harder to access again. Money invested may fall in value just when it is needed. A single smooth investment return does not measure either the chance or severity of a market loss.

Keep the household’s cash reserve, other debts and near-term goals in the decision. If extra payments would leave no room for a repair, parental leave or a period without work, test the combination in a scenario. The Zenarios repay-versus-invest report places the choice inside the household forecast.

Read rent versus buy for the broader housing decision, debt payoff strategies for multiple debts and market simulations for uncertainty beyond a constant rate.

Common questions

How does this compare overpaying a mortgage with investing?

Both paths use the calculated regular mortgage payment plus the same extra monthly amount. One overpays the loan; the other invests the extra. After either loan clears, its whole monthly budget is invested. Results compare investments after the entered gains tax minus remaining mortgage debt.

Is home value included in the comparison?

No. The same home is held under both choices, so its value cancels out of their difference. The displayed investments-minus-debt figure is not your complete household net worth. Investment tax is applied only to positive gains at the comparison date.

Does the calculator include repayment penalties and tax deductions?

No. It assumes a fixed mortgage rate, no overpayment restrictions or charges, and no mortgage-interest tax deductions. Check your loan terms and local tax rules before using the comparison for a real decision.

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Written by the maker of Zenarios, a software engineer. These guides explain planning concepts and the product; they are not a personalized financial recommendation. Illustrative calculations are not results from your plan.