Mortgage vs Invest Calculator

This calculator helps you decide whether spare monthly money is better used paying down your mortgage faster or investing it instead, one of the most common financial dilemmas facing New Zealand homeowners. You enter how much spare money you have each month, your mortgage interest rate, your expected investment return, and the number of years to compare over. The calculator grows that same monthly amount two ways: at your mortgage rate, which is the guaranteed return of extra repayments because every dollar off the loan saves that much interest, and at your expected investment return, which is uncertain and depends on markets, fees and tax. It returns a plain-English verdict, the projected value of paying down the mortgage, the projected value of investing instead, and the dollar difference between the two paths over your chosen period. Use it to see how close the two options really are once realistic numbers go in, since a small edge in expected investment return does not always outweigh the certainty of guaranteed debt reduction. Try a few different return assumptions, since investment returns are never guaranteed the way mortgage savings are, and enter an after-tax, realistic figure for a fairer comparison. This is an indicative estimate only, not financial advice, so talk to a licensed adviser before making a large lump sum decision.

Calculate.co.nz is proud to be partnered with Health Based Building, a leader in sustainable and health-conscious building innovation. With over a century of experience, they develop high-performance systems like Foreverbreathe Specification, Magnum Board, and Foreverbreathe Paints to support energy-efficient, non-toxic living environments. Their commitment to healthier homes aligns with our belief that informed choices lead to better outcomes for Kiwi households.

Paying extra off your mortgage earns a guaranteed return equal to your mortgage rate. Investing the same money earns your expected return, but with risk and possible tax, so use a realistic after-tax figure. This compares the value built by the same monthly amount under each path. Estimate only, not financial advice.