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How Cost Segregation Actually Works: A Real Numbers Example for Dentists

by PracticeCFO | April 24, 2026
Two people work on finances, using a calculator and reviewing documents on a table. An apple and striped cloth add a casual touch.

The best way to understand cost segregation is to run the numbers. In Episode 151 of The Dental Boardroom, Wes Read walks through a real-world example using a dentist collecting $1.2 million per year. Here is how the money flows.

The Dental S-Corp Side

Start with the dental practice, which operates as an S-Corporation:

●   Collections: $1,200,000

●   Clinical expenses (labor, labs, supplies, marketing, admin): $600,000

●   Rent paid to the Real Estate LLC: $170,000 ($14,167/month)

●   Net K-1 income to the dentist: $430,000

The $170,000 in rent is fully tax-deductible inside the S-Corp. It reduces the dentist's taxable K-1 from what would have been $600,000 down to $430,000 — a direct reduction of taxable income.

The Real Estate LLC Side

Now look at what happens inside the building LLC:

●   Rental income: $170,000

●   Mortgage interest (deductible portion): $80,000

●   Net income before depreciation: $90,000

Without cost segregation, the dentist might take a standard depreciation deduction of $40,000 to $50,000, leaving $40,000 to $50,000 of taxable income from the LLC.

With cost segregation applied in year one: $200,000 of depreciation.

●   $170,000 rent income

●   Less $80,000 mortgage interest

●   Less $200,000 cost segregation depreciation

●   Net result: a loss of $110,000 in the LLC

The dentist owes zero taxes on the rental income. The rent is, effectively, tax-free income.

The Spouse Strategy: Unlocking the Full Loss

That $110,000 loss does not disappear. Under normal passive activity rules, it is suspended and can only offset future passive income. But there is an exception.

If the dentist's spouse qualifies as a real estate professional — working more than 750 hours per year in real estate activities, with real estate being their primary professional activity — all passive losses from the LLC can be used to offset any income, including the $430,000 K-1 from the dental practice.

The result: the dentist is effectively paying taxes on $320,000 of income instead of $430,000. That is a six-figure reduction in the tax base, entirely legal, and powered by a building the dentist already owns.

What This Means in Practice

The cost segregation strategy does two things simultaneously. Inside the S-Corp, the rent payment lowers K-1 taxable income dollar for dollar. Inside the LLC, the depreciation generated by the cost segregation study wipes out the rental income — and then some. If the spouse qualifies, the excess loss flows through to reduce dental practice income as well.

This is not a loophole. It is a deliberate part of the tax code, available to every dentist who owns their building and structures it correctly.
Listen to Episode 151 of The Dental Boardroom Podcast: https://podcasts.apple.com/us/podcast/151-cost-segregation-tax-strategy-for-dentists-part-3/id1518344747?i=1000761386035

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