The Section 481(a) Adjustment: Your Catch-Up Depreciation Explained

When you change your depreciation method via Form 3115, you need a way to account for the difference between what you've been deducting and what you should have been deducting. That mechanism is the Section 481(a) adjustment — and for cost segregation look-backs, it's almost always a large, single-year deduction in your favor.

What Is a Section 481(a) Adjustment?

IRC § 481(a) requires that when a taxpayer changes an accounting method, the IRS must compute an adjustment to prevent items of income or deduction from being duplicated or omitted. In plain English: you need to true up the books so that changing methods doesn't let you skip deductions or take them twice.

For cost segregation, the 481(a) adjustment is always "negative" (favorable to you). That's because straight-line depreciation underestimates true deductions — so the catch-up is always additional depreciation you're now claiming.

How the Adjustment Is Calculated

Here's a simplified example. Suppose you purchased a short-term rental for $500,000 in 2022. Under straight-line, you've been depreciating $18,182/year ($500,000 ÷ 27.5) for 3 years, claiming $54,546 total.

A cost segregation study reclassifies $120,000 to 5-year property and $40,000 to 15-year land improvements. Under MACRS with 80% bonus depreciation (applicable in 2022), you should have taken: $96,000 in bonus depreciation on the 5-year property in 2022, plus accelerated MACRS on the 15-year property, plus straight-line on the remaining structure. When fully recomputed, you should have claimed approximately $130,000 over those three years — not $54,546.

The 481(a) adjustment is the difference: $130,000 − $54,546 = $75,454. That entire amount is your current-year deduction in the year you file Form 3115.

Tax Impact: How Much Does It Actually Save You?

If you're in the 37% federal tax bracket and have a $75,000 481(a) adjustment, you're looking at roughly $27,750 in direct federal tax savings — potentially more if you also offset state taxes. Add in the deduction for the current year's accelerated depreciation going forward, and the compound effect over several years is substantial.

For STR investors who qualify for the STR tax loophole, these deductions can offset W-2 income dollar-for-dollar — which makes the math even more powerful since there's no passive loss limitation.

The 481(a) and Bonus Depreciation: A Common Question

Some investors wonder whether the 481(a) catch-up amount itself qualifies for today's 100% bonus depreciation rate (post-OBBBA). The answer: the catch-up uses the bonus rates applicable to the year each asset was placed in service. You can't retroactively apply 2025's 100% rate to an asset bought in 2022 when 80% was the applicable rate.

However, for properties placed in service in 2025 (on or after January 19), a look-back study done within the same tax year can absolutely apply 100% bonus depreciation — because the placed-in-service date is recent enough to use the current rate.

Does the Adjustment Affect Your Basis?

Yes. When you take additional depreciation via the 481(a) adjustment, it reduces your adjusted cost basis in the property. This matters at sale: you'll have a higher amount of Section 1250 gain subject to recapture (at a maximum 25% rate). This is not necessarily a reason to avoid cost segregation — most investors are better off having the deduction now — but it's something to plan for with your CPA.