Cost Segregation Study in Montana for Airbnb and Short-Term Rental Investors

Montana's individual income tax conformity runs through MCA 15-30-2101 (which defines the "Internal Revenue Code" by rolling reference to the version "as amended," rather than a fixed historical date) together with MCA 15-30-2120, the statute listing the specific additions and subtractions individual and pass-through filers must make to federal taxable income to arrive at Montana taxable income — and that list, as currently published, does not include a bonus-depreciation add-back. Montana's separate corporate income tax statute, MCA 15-31-113, conforms C-corporations to "the federal Internal Revenue Code in effect for the taxable year" on its own rolling basis, but it governs C-corporations only; it does not itself establish, and should not be cited as, the conformity rule for individuals or pass-through owners such as partners, S-corp shareholders, or sole proprietors. Together, MCA 15-30-2101 and 15-30-2120 mean that for most individual and pass-through Montana filers, the accelerated first-year deductions produced by a cost segregation study under IRC Section 168(k) — including the 100% bonus depreciation the One Big Beautiful Bill Act (OBBBA) restored for qualifying property acquired after January 19, 2025 — generally reduce Montana taxable income in the same year they reduce federal taxable income, consistent with current Montana Form 2 instructions and with no separate state add-back required under current law. Some general online tax-conformity summaries still describe Montana as decoupled from bonus depreciation, which appears to reflect an older, since-superseded rule rather than current statute; because conformity guidance can change and sources disagree, confirm the current-year treatment against the Form 2 instructions with a CPA before you rely on it for planning.

Montana also carries a real, if modest, individual income tax: the top marginal rate steps down from 5.9% to 5.65% for 2026 and to 5.4% for 2027 under House Bill 337, with a lower 4.7% bracket for income below the top threshold. Because bonus depreciation generally flows through, an accelerated deduction from a cost segregation study reduces income taxed at those state rates in addition to your federal liability — real dollars, not a moot point the way it would be in a state with no income tax at all.

Property tax is where Montana's 2026 overhaul becomes directly relevant to rental owners. Under House Bill 231 and Senate Bill 542, Montana rebuilt its residential property tax structure for 2026: primary residences and long-term rentals (leases of 28 days or more, occupied at least seven months a year) qualify for a tiered rate that starts at just 0.76% of value for the lowest tier but climbs to 1.90% for the portion of a home's value at or above four times the statewide median residential value, while second homes and short-term rentals — including Airbnbs, VRBOs, and cabins — are taxed at a flat 1.90% rate on their entire value, with no lower starting tier. In other words, a short-term rental owner pays, from dollar one, the same 1.90% ceiling a high-value primary residence only reaches once it crosses that four-times-median threshold. For an investor running a short-term rental, that flat 1.90% rate applied to the full value is exactly the kind of ongoing expense that accelerated depreciation from a cost segregation study is well suited to help offset.

Without a study, the IRS defaults you to depreciating an entire residential rental building on a straight-line basis over 27.5 years, or 39 years for a commercial property, and that pace of write-off has nothing to do with how the building's components actually wear out. A cost segregation study is an engineering-based analysis that walks through your property's construction records, cost documentation, and physical components — flooring, cabinetry, decking, appliances, specialty electrical, exterior improvements like driveways and landscaping — and reclassifies the pieces that qualify into 5-year, 7-year, and 15-year recovery classes under IRS-approved methods (typically cost estimation combined with engineering review). Those shorter-lived components are what become eligible for bonus depreciation. Under the OBBBA, signed into law in July 2025, qualifying property acquired after January 19, 2025 can claim 100% bonus depreciation on those reclassified components, meaning the full amount can be deducted in the year the property is placed in service rather than spread across the standard depreciation schedule. The acquisition-date test itself turns on when you entered a binding written contract to purchase the property (or, for new construction, when construction began), not simply your closing date or placed-in-service date — so a property that closes in 2026 under a contract signed before January 19, 2025 may not qualify for the 100% rate. Confirm your specific purchase timeline against this test with a tax advisor.

For illustration only — your results depend on your property and tax situation, and this is not a projection of actual savings.

Say an investor buys a $650,000 short-term rental cabin near Whitefish, close to Glacier National Park. Allocating roughly 20% of the purchase price to land leaves a $520,000 depreciable building basis. A cost segregation study might identify around $145,000 of that basis — flooring, furnishings-adjacent fixtures, decking, a hot tub pad, exterior lighting, and site improvements — as qualifying for 5-, 7-, or 15-year treatment instead of the standard 27.5-year residential schedule. Under 100% bonus depreciation, that entire $145,000 could be deducted in year one instead of trickling out over decades, generating a large first-year loss that can offset other rental income (and, for owners who qualify for the short-term rental material participation strategy discussed below, potentially other active income too). Again, these are round, illustrative numbers — actual reclassified amounts depend on the engineering study, and actual tax benefit depends on your income, basis, and filing situation.

If you bought or renovated your Montana property in a prior tax year and never had a cost segregation study performed, you have not missed the opportunity. A look-back study lets you catch up on the depreciation you could have claimed without amending a single past tax return. The mechanism is IRS Form 3115, Application for Change in Accounting Method, which allows you to correct your depreciation method and claim the entire missed amount as a one-time Section 481(a) adjustment in the current tax year. For a Montana rental owner who has held a property for several years, this can mean a substantial current-year deduction generated from depreciation that was always available but never claimed.

• Short-term rental and Airbnb hosts operating in Montana's established vacation-rental markets — Whitefish and Big Sky near Glacier and Yellowstone National Parks, plus Bozeman, West Yellowstone, Red Lodge, and Livingston — where nightly-rate income can be substantial but the new 1.90% short-term-rental property tax rate adds real carrying cost
• Long-term rental property owners in Missoula, Billings, Kalispell, or Helena who may also qualify for Montana's reduced 2026 long-term-rental property tax tier and want to pair that with accelerated federal and state depreciation
• Investors who recently purchased or renovated a Montana rental property, since acquisition and renovation costs are exactly what a cost segregation study is built to analyze
• High-income W-2 earners or business owners exploring the short-term rental material participation strategy, which requires an average guest stay of seven days or less and material participation in operating the property — a federal income-tax test that is separate from Montana's 28-day threshold for the property-tax long-term-rental classification, and worth understanding as two distinct rules before you set your rental strategy
• Owners weighing a sale or 1031 exchange who want to understand their current depreciation position, including any recapture exposure, before deciding on next steps