Pay Off Debt or Invest Calculator

As a rule of thumb, compare your debt's interest rate to the return you realistically expect from investing. If your debt costs more than you'd earn — high-interest credit cards at 18–25% almost always do — paying it off is a guaranteed, tax-free return and the clear winner. If the debt is cheap (a sub-5% mortgage or student loan) and you have a long horizon, investing the spare cash usually builds more wealth. This calculator runs both paths month by month on your actual numbers so you don't have to guess where the line falls.

Every dollar you put toward a debt saves you that debt's interest rate, for certain. Paying off a 20% credit card is mathematically identical to earning a guaranteed 20% return — with no risk and no tax. An investment expected to return 8% might return 20% or lose 10% in any given year. That certainty is why paying off high-interest debt beats investing even when the headline investment return looks higher.

It simulates two strategies over your chosen horizon. In 'pay debt first', all your spare cash goes to the debt on top of the minimum until it clears, then the whole freed-up payment is invested for the rest of the horizon. In 'invest first', you pay only the minimum and invest the spare cash from day one. Each month it accrues debt interest and compounds investment returns, then compares the final net worth (investments minus any remaining debt) — expressed in today's money after inflation.

It compares expected average outcomes, not guaranteed ones. Paying down debt is a certain return; the investment figure assumes your expected return actually materializes, which it may not, especially over short horizons. When the two strategies are within a point or two, clearing the debt is the safer choice even if the model gives investing a narrow edge. Treat the result as the average case and weigh your own risk tolerance.