Extra Mortgage Payment vs Invest Calculator

About this calculator

This comparison runs two amortization paths side by side: one where extra principal goes straight onto your mortgage each month, shortening the loan and cutting the interest you would otherwise pay on the remaining balance, and one where that same money is invested instead and left to compound at an assumed rate of return over the same period. The mortgage path is a guaranteed return equal to your loan's interest rate, since every dollar of prepaid principal is a dollar you will never pay interest on again. The investing path is an uncertain return that depends on markets, but is typically expected to be higher over long horizons and, unlike home equity, stays liquid and accessible.

Homeowners run this calculation when they have spare cash each month and are deciding between debt payoff and building an investment portfolio, particularly after a raise, a bonus, or once other higher-interest debt is cleared. The decision usually tips toward extra payments when the mortgage rate is high relative to expected investment returns, when the borrower values the certainty and peace of mind of a paid-off home, or when they are risk-averse and close to retirement; it tips toward investing when the mortgage rate is comparatively low, the money can go into a tax-advantaged account, or the borrower has a long time horizon and can tolerate market volatility.

This calculator amortizes your mortgage under both scenarios and reports the interest saved and time shaved off the loan from extra payments against the projected balance of investing the same cash, so you can see the numeric trade-off before choosing a path.