If you've read anything about accelerating depreciation on a rental, you've run into two terms that get used almost interchangeably: bonus depreciation and Section 179. Both let you deduct the cost of qualifying property up front instead of spreading it across decades. But for residential rentals they are not the same tool, and treating them as equivalent, or reaching for the wrong one, can leave a real deduction stranded. Here's the difference that actually decides it, with the numbers.
They do the same thing, until they don't.
Bonus depreciation (Internal Revenue Code §168(k)) and Section 179 both pull deductions forward. A cost segregation study feeds either one: it moves carpeting, cabinetry, appliances, specialty electrical, decorative finishes, and land improvements out of the 27.5-year bucket that residential real estate normally sits in, and into 5-, 7-, and 15-year buckets. Once those assets are reclassified, either tool can expense them in the year you place the property in service.
The One Big Beautiful Bill restored 100% bonus depreciation for property acquired (contract signed) and placed in service after January 19, 2025, and separately raised the Section 179 expensing cap to $2.5 million. On paper, both look generous. The difference shows up in what each one is actually allowed to do.
The one rule that decides it: can it create a loss?
This is the whole ballgame. Section 179 cannot create or increase a loss. Your deduction is capped at your aggregate net income from the active conduct of all your trades and businesses for the year (under the regulations that can include W-2 wages — though a passive rental's income may not count as active conduct at all). Expense down to that limit, and the unused remainder carries forward to a future year. Bonus depreciation carries no income limitation. It can drive a rental to a paper loss, and that loss is usually the entire point of accelerating depreciation in the first place.
So the question is rarely "which gives a bigger first-year deduction", both can expense the same asset. The question is whether you need the deduction to create a loss you can use against other income. If you do, Section 179 won't get you there by design. Bonus will.
The math, for a $525K single-family rental.
Take a typical acquisition: $525K all-in, roughly $420K of depreciable basis once land is excluded. A reasonable residential study reclassifies around 22% of that basis, call it $92K, into 5-, 7-, and 15-year property. Now say the rental nets $18K of income before depreciation.
Under Section 179, your deduction is capped at your active-conduct business income for the year — assume for illustration that limit works out to the rental's $18K. You expense $18K of the $92K this year, zero out the rental's income, and carry the other $74K forward to a year that has income to absorb it. No current-year loss.
Under bonus depreciation, the full $92K comes off this year. The $18K of income becomes a $74K loss. At a 32% marginal federal rate, the $92K bonus deduction is worth roughly $29,400 if you can use it in full, against about $5,760 from the Section 179-capped $18K, with the rest deferred.
One candid caveat, because it matters: that $74K bonus loss is passive by default. On a long-term rental it's suspended under the passive activity rules and waits until you have passive income or sell, unless you qualify as a real estate professional. The short-term rental exception, where you materially participate in an STR, or real-estate-professional status is what turns that paper loss into a deduction against W-2 or other active income. Without one of those, the loss isn't lost. It's just parked. (For more on why the restored 100% schedule changed this math, see our note on bonus depreciation coming back.)
So when is Section 179 the better call?
It isn't never. Three situations where Section 179 earns its place on a residential rental:
You don't want a loss. If you have rental income you'd like to wipe out but no way to use a passive loss this year, Section 179 expenses exactly enough to bring income to zero and parks the rest, cleaner than generating a suspended loss you can't touch.
You want surgical control. Section 179 lets you expense one specific asset, or even part of one. Bonus depreciation is all-or-nothing within an asset class. You elect out class by class, not asset by asset. If you want to fully expense a new HVAC unit but keep depreciating everything else, Section 179 is the scalpel.
State conformity. A number of states decouple from federal bonus depreciation but still allow Section 179, sometimes at a lower state cap. In those states, Section 179 can rescue a first-year deduction the state would otherwise force you to stretch out.
One hurdle to flag: Section 179 requires the property be used in the active conduct of a trade or business, and a passive residential rental doesn't always clear that bar. Bonus depreciation has no such requirement, which is one more reason it tends to be the default for rental investors.
Can you use both on the same property?
Yes, and the ordering is fixed: Section 179 is applied first, then bonus depreciation on whatever basis remains, then ordinary MACRS depreciation on the rest. For most residential investors, though, the honest answer is that bonus depreciation alone does the job. The $2.5 million Section 179 cap almost never binds on a 1-4 unit rental, and the income limitation usually makes it the weaker tool. We reach for Section 179 only in the specific cases above.
What to do with this.
The practical takeaway: for a residential rental where you want the deduction to actually offset other income, bonus depreciation is almost always the right tool, and a cost segregation study is what generates the short-life basis to apply it to. Section 179 is a useful complement in a handful of spots, not a substitute. Run your own numbers first; our savings estimate gives you a rough year-one figure in about a minute. Every study we deliver is reviewed by a licensed tax professional and built audit-ready, with the asset-by-asset detail your CPA needs to make the bonus-versus-179 election cleanly.