What it means
Headline numbers mislead whenever tax treatment differs. A 6% taxable bond and a 4.5% tax-exempt bond cannot be ranked by their coupon rates alone, because the investor never keeps the whole 6%.
Converting to an after-tax basis puts both options into the same unit: money the holder actually keeps. Once that conversion is made, ranking the options is arithmetic rather than argument.
The same logic applies on the cost side of the business. Interest on debt is generally deductible, so a 9% loan has an after-tax cost of 9% x (1 - 0.25), or 6.75%, at a 25% tax rate, whereas a dividend paid on equity carries no such deduction.
The rate you use is the marginal rate, not the average rate, because you are analysing the tax on the next dollar of income rather than the tax on all income to date. Using an average effective rate here understates the tax on incremental returns and skews the comparison.
Timing is the nuance most people miss. Two investments with the same after-tax return are not equivalent if one is taxed each year and the other defers tax until sale, because the deferred option compounds on money that would otherwise have gone to the tax authority.
In practice
Real-world examples.
Example
A finance director compares a 9% bank loan with an 11% preference share issue. On an after-tax basis at a 25% tax rate the loan costs 6.75% while the preference dividend still costs 11%, which settles the decision quickly.
Example
An employee is offered a $6,000 taxable bonus or a $4,800 tax-free benefit. At a 35% marginal rate the bonus is worth $6,000 x 0.65 = $3,900 after tax, so the smaller tax-free benefit is worth $900 more in the hand.
Example
A property investor compares rental yield with dividend yield on a listed fund. Because rental profits and dividends attract different rates in her jurisdiction, she converts both to an after-tax basis before deciding, and the ranking flips from the pre-tax comparison.
Formula
Calculation
After-tax amount = pre-tax amount x (1 - marginal tax rate)
After-tax yield = pre-tax yield x (1 - marginal tax rate)
Taxable equivalent yield = tax-free yield / (1 - marginal tax rate)
Worked example. An investor with $200,000 to place and a 30% marginal tax rate compares a corporate bond yielding 6.5% with a tax-exempt municipal bond yielding 4.2%.
Corporate bond interest = $200,000 x 0.065 = $13,000
Tax on that interest = $13,000 x 0.30 = $3,900
After-tax income = $13,000 - $3,900 = $9,100
After-tax yield = $9,100 / $200,000 = 0.0455, or 4.55%
Municipal bond income = $200,000 x 0.042 = $8,400, with no tax, so the after-tax yield is 4.2%.
The corporate bond wins by $9,100 - $8,400 = $700 a year. Viewed the other way round, the taxable equivalent yield of the municipal bond is 4.2% / (1 - 0.30) = 6.0%, so the corporate bond only wins because it yields more than 6.0%. If the investor's marginal rate rose to 40%, the municipal bond's taxable equivalent yield would become 4.2% / 0.60 = 7.0% and the ranking would reverse.Case study
Seen in the real world.
Braemore Family Holdings is an illustrative, fictional investment company managing $12,000,000 for three generations of one family. Its investment committee had always ranked opportunities by headline yield, and its portfolio was accordingly heavy in taxable corporate bonds.
A new adviser rebuilt the comparison on an after-tax basis. The family trust faced a 37% marginal rate, so a corporate bond yielding 5.8% returned 5.8% x 0.63 = 3.65% after tax, while a municipal portfolio yielding 4.0% returned the full 4.0%. On $12,000,000 the difference was 0.35% x $12,000,000 = $42,000 a year, in favour of the lower headline yield.
The committee shifted $7,000,000 into tax-exempt holdings and adopted a rule requiring every proposal to be presented in both pre-tax and after-tax terms. In this illustrative case nothing about the risk of the underlying assets had changed; the family had simply been ranking options in the wrong unit of measurement.
Watch out
Common mistakes.
- Using the average effective tax rate instead of the marginal rate. Incremental income is taxed at the margin, so the average rate understates the tax on the next dollar earned.
- Comparing pre-tax yields across differently taxed products. A tax-exempt yield and a taxable yield are not in the same unit and cannot be ranked side by side.
- Ignoring the timing of tax. An investment taxed only on sale compounds faster than one taxed annually at the same headline rate.
Questions
People also ask.
How do I convert a tax-free yield for comparison?
Divide it by one minus your marginal rate, which gives the taxable yield that would leave you equally well off.
Does the after-tax basis apply to costs as well as returns?
Yes, and it is central to the cost of capital, because deductible interest costs less after tax than a non-deductible dividend of the same size.
Whose tax rate should be used?
The rate of whoever actually bears the tax, which is the company for corporate decisions and the individual for personal ones, and the two can differ sharply.
From the founder's library
Take it further with the book.
Build your financial confidence beyond this definition. Shihan's full-length guide, Accounting Fundamentals, takes the same plain-English approach and turns it into a complete, practical playbook for non-finance managers, business owners and students - with chapter-end quiz answers and presentation slides included.
25% off with code MMHQ25, applied at checkout. Priced in USD - checkout may show the equivalent in your local currency.
View the book and save 25%Related