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Discounting a Perpetual Debt Tax Shield

Article Quant Q&A · Author: Aqqqq
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Summary

The document asks why the present value of the tax shield from constant, perpetual debt is expressed as the corporate tax rate times interest payment divided by the expected return on debt. The response characterizes the expected return as the discount rate applied to the interest-related tax benefit. In this interpretation, dividing the recurring tax saving by the required return converts a perpetual stream into a present value.

The explanation is brief and does not derive the formula step by step or specify assumptions about risk, taxes, debt pricing, or whether the discount rate should reflect the tax shield’s own risk. It also does not distinguish expected return from yield or discuss how debt market movements affect the valuation. The note therefore conveys the denominator’s discounting role, but readers seeking a full corporate finance derivation or a treatment of changing debt balances will need additional material.

Key ideas

  • The tax shield from interest is the recurring tax benefit associated with debt payments.
  • The expected return on debt is presented as the discount rate for valuing that perpetual stream.
  • The response gives an intuition for the denominator rather than a complete valuation derivation.
  • The excerpt does not specify risk, tax, or debt-market assumptions underlying the formula.

Tags

Fixed incomeRisk management
Full text
# How is the present value of tax shield of constant and perpetual debt derived?


# How is the present value of tax shield of constant and perpetual debt derived?












According to this site, the present value of tax shield of constant and perpetual debt is:

corporate tax rate × interest payment ÷ expectd return on debt

I understand the part about "corporate tax rate × interest payment". But why is expectd return on debt be divided here? (I think that it is also not from summing geometric sequence.)

## Answer by TiKa (score 0)

https://quant.stackexchange.com/a/58780

Interest payment is determined by the bond (either fixed or variable), expected return varies according to market movements. It is effectively the discount factor.

Shown in full with attribution under the source's licence. Licence: CC BY-SA 4.0 (Stack Exchange)

This summary was written by Stratmill's research agent from the original; it is not a copy of the source.