After-tax Cost of Debt Calculator

Written by Great Medico

Updated September 25, 2026 •2 min read

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A result from After-tax Cost of Debt Calculator becomes more meaningful when the source numbers and formula stay visible. That makes it easier to reproduce the calculation instead of relying on an unexplained figure.

What this calculator does

After-tax Cost of Debt Calculator estimates the effective cost of debt after applying the entered marginal tax rate to the pre-tax borrowing cost. It works from pre-tax cost of debt and marginal tax rate. For After-tax Cost of Debt Calculator, because no outside market data is inserted, the result stays tied to the exact assumptions visible on the page.

How to use it

Use the form to supply Pre-tax cost of debt and Marginal tax rate. For After-tax Cost of Debt Calculator, enter percentage or rate fields on the scale displayed by the form rather than converting them to an unstated format. Before calculating, recheck Pre-tax cost of debt, Marginal tax rate against the source numbers you intend to analyze.

How the calculation works

After-tax cost of debt = pre-tax cost of debt × (1 − tax rate). The After-tax Cost of Debt Calculator result follows the stated equation and the form values relevant to that calculation. For After-tax Cost of Debt Calculator, the result is only meaningful for the exact values supplied, so input errors should be corrected before interpretation.

Example

A 6% pre-tax cost of debt and 25% tax rate give an after-tax cost of 4.5%. The After-tax Cost of Debt Calculator example is a math check only; your result should come from the values entered on the form.

How to interpret the result

The difference between pre-tax and after-tax cost represents the simplified interest tax shield used in many WACC calculations. For a clean comparison with After-tax Cost of Debt Calculator, keep the displayed input definitions and measurement basis consistent across scenarios.

Limitations and notes

The formula assumes interest is tax-deductible at the entered rate. Actual deductions can be limited by tax law, losses, jurisdiction, debt type, or company-specific circumstances, and this calculator does not estimate those constraints. Recalculate After-tax Cost of Debt Calculator when the source values entered on the form change materially.