After-Tax Cost of Debt

Short definition

After-tax cost of debt is all-in interest after the cash tax shield on the deductible part. It is the debt leg of WACC; without a shield, Kd stays as is.

Detailed explanation

T is not the statutory rate; it is whether that interest actually cuts the tax base and cash tax. Losses, exemptions, thin-cap and unused capacity pull T to zero.

The same economics as after-tax Kd in the banking/WACC set, with the tax side stressed: without deductibility and tax capacity the formula does not run. In a high-rate period Kd can look above Ke; if the shield is not cash, equity is not “expensive” by comparison — cash Kd is still high.

Why it matters for the CFO

If debt is sold as “cheap after tax”, WACC is wrong until cash T and the thin-cap cap are locked.

How it is calculated

Kd_after = Kd_all-in × (1 − T_nakit) (yalnızca indirilebilen faiz için)

All-in Kd includes fees and the reference. T applies only to deductible interest times the true cash tax rate.

Variables in the formula

• Kd: all-in cost of debt
• T: marginal cash tax rate actually paid or payable

How to read it

The shield Kd × T exists only on the slice that is deducted and that produces cash tax. A sustainable shield is not a one-year carry-forward.

Numerical example

All-in Kd 48%, all interest deductible and cash T = 25% → after-tax ≈ 36%. If cash tax is zero because of a carry-forward, ≈ 48%.

Definitions are educational. They are not investment, credit or tax advice.