What Is a Good Debt vs Bad Debt Calculator?

A good debt vs bad debt calculator replaces the folk labels with arithmetic. The idea that a mortgage is good debt and a credit card balance is bad debt is useful shorthand, but the labels confuse the product with the price. What actually separates them is a single comparison: the after-tax cost of the borrowing against the return the borrowed money produces. When the return exceeds the cost, the debt creates value each year it is carried; when it does not, it destroys value, and the label is irrelevant.

Framing debt this way also exposes the cases the labels get wrong. A low-rate mortgage financing an appreciating home can still be bad debt for a household that cannot carry it through a downturn, while a student loan at a modest rate becomes good debt only if the degree raises earnings by more than the interest. High-rate consumer debt is almost always bad in the arithmetic sense, because few safe investments clear a 20%-plus hurdle after tax.

How It Works

The calculator reduces the debt's rate for any tax benefit: the deductible share of the interest multiplied by your marginal tax rate gives the percentage-point subsidy, which is subtracted from the headline APR. That produces the after-tax cost of the debt. It then compares it with the expected return on the borrowed funds — the investment yield, or the appreciation rate of the asset the borrowing financed — to produce the annual spread.

Over the horizon you set, the calculator totals the after-tax interest paid and the value created by the borrowed money on a straight-line basis, and reports the difference as the net benefit. The spread drives the verdict: two percentage points or more is good debt, between zero and two is neutral, and a negative spread is bad debt — borrowing that costs more than it earns every year.

Understanding Your Results

The primary card reports the net benefit over the horizon with the verdict and the annual spread. The three-stat bar shows the after-tax cost of the debt, the expected return and the annual interest bill, and the breakdown table separates the two flows — interest paid and value created — so the net figure can be audited line by line. Summary Statistics adds the tax benefit in percentage points and the break-even return: the rate the borrowed money must earn for the debt to be value-neutral.

Treat the model as a first-order screen, not a guarantee. It assumes the borrowed money earns its expected return every year and that the debt is carried rather than amortized, which fits a long-horizon mortgage comparison better than a five-year car loan. Risk cuts both ways under leverage: volatile investments can lose money for years while the interest arrives monthly without fail, so test the spread against a worst-case return as well as an average one. If the debt only works at optimistic returns, it is not good debt — it is a bet. Review the spread whenever rates move at renewal, because a quarter-point change in either direction can flip the verdict on a marginal balance.