@nicolelapin: Most personal finance advice treats your money decisions like a math problem but this one actually is a math problem.. and then it’s a you problem. The gap between a 4% mortgage rate and an 8% market return is real money over time. The issue is that gap only pays off if the “extra” cash goes straight to work in an index fund, month after month, automatically. Behavioral finance has a whole body of research on what happens when money sits loose in a checking account. Spoiler: it doesn’t stay there. Knowing which move is right comes down to one honest question about your own habits. Not your intentions, but your actual pattern. The math favors investing the difference and your spending history has a vote too.

Nicole Lapin

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Tuesday 14 July 2026 17:17:01 GMT