Pay Off Debt vs Invest Calculator

About this calculator

Whether spare cash is better spent paying down debt or put into the market comes down to comparing a guaranteed return against an expected return: every dollar used to pay off debt earns a certain, risk-free return equal to that debt’s interest rate, while every dollar invested earns an uncertain return that must first be adjusted for taxes and, arguably, for the risk of loss. If your investment’s expected after-tax return exceeds your debt’s interest rate, investing wins on paper — but the debt payoff route removes risk entirely, which is worth something the pure math doesn’t capture.

Personal finance planners and everyday borrowers run this comparison constantly, especially with credit card debt (often 20%+ APR, which almost no diversified investment reliably beats) versus low-rate mortgage or student debt (often below typical long-run stock market returns), where the “right” answer can flip entirely based on the rate. The after-tax adjustment matters too — investment gains are taxed, so a nominal 8% return might behave more like 6% net of capital gains tax, changing the comparison.

This calculator takes your spare cash, your debt’s interest rate and your expected investment return (with a tax adjustment) and shows which path leaves you with more money, so you can decide with the numbers in front of you rather than a rule of thumb.