Picture this. You own a vacation rental a few blocks off Market Square — a restored colonial within walking distance of the working waterfront, Strawbery Banke, and one of the most celebrated restaurant scenes in New England. It rents well through the Seacoast summer. And here’s the part most owners don’t fully price in: when the depreciation deduction lands, New Hampshire takes nothing.
That’s the Portsmouth play in one sentence: a cost segregation study can produce a large Year-1 deduction, and in a true zero-income-tax state, that deduction lands undiluted.
Why New Hampshire’s zero-tax posture matters
Here’s the insight that’s new for 2025: New Hampshire is now a true zero-income-tax state. It never taxed wages, but it did tax investment income through the Interest & Dividends tax. That tax was fully repealed effective 2025 — so there is no longer any state layer sitting on top of your federal return.
That’s a genuine rarity in high-tax New England. New Hampshire is ringed by Massachusetts to the south, Maine to the north, and Vermont to the west — all three of which tax income. A Seacoast owner keeps the full federal + NIIT benefit with no state clawback, while a neighbor an hour south in Massachusetts pays a state layer on the same dollar. For a high earner weighing where to hold rental real estate, that gap compounds every year the asset is depreciated, not just in Year 1.
For cost segregation, that matters because the deduction’s value is your combined marginal rate times the reclassified dollars. Remove the state layer and the math is clean: federal 37% + NIIT 3.8% = ~40.8%, with nothing eroding it.
Who’s buying — and the combined rate
Portsmouth’s buyer pool is distinct. It’s Boston-area professionals trading the Massachusetts tax posture for the Seacoast lifestyle and a 0% state rate; second-home owners drawn to the colonial downtown, New Castle, and the Rye coastline; and tourism and coastal vacation-rental investors capitalizing on a walkable, restaurant-driven market. All of them face the same simple stack:
Verify with your CPA — combined-rate math depends on filing status and AGI thresholds for NIIT.
What we study on the Seacoast
Portsmouth’s inventory is varied, and cost segregation reaches most of it. We study coastal vacation rentals along the Rye and New Castle shoreline, historic downtown rentals in and around Market Square and The Hill, single-family rentals, and small multifamily buildings in the South End and Atlantic Heights. The colonial building stock here often carries more reclassifiable finish work than a generic new build — restored casework, built-ins, and site improvements that read straight into 5- and 15-year property. Second-home conversions can also qualify once they become rentals, valued at the lower of cost or fair market value at conversion — a nuance worth confirming with your CPA.
A representative worked example
A representative Portsmouth Seacoast vacation rental — a restored home near the waterfront — is purchased for $690K. After land and setup, the property carries a $520,000 adjusted basis. An engineering-method study breaks that basis into roughly $96K of 5-year assets (appliances, hot tub and pool equipment, decorative lighting, casework and built-in furnishings, audio-visual), about $3K of 7-year property, and $47K of 15-year land improvements (decking, hardscaping, walkways, outdoor lighting, and site work).
That’s $146K reclassified into accelerated depreciation — roughly 28% of the $520,000 depreciable basis — in Year 1. At ~40.8%, federal + NIIT savings come to about $60,000.
The deductibility nuance sits right here: for a short-term rental (an average guest stay of 7 days or less), the loss can offset your W-2 or business income if you meet the material-participation test — 100 hours of material participation where no one else participates more. For a long-term rental, the deduction generally shelters that property’s rental income and any unused loss carries forward to future years. Confirm which path applies with your CPA.
Portsmouth vs. Boston and Cambridge
Owners often ask how the Seacoast compares to the metro just south. The engineering is identical — we split the depreciable basis into 5-, 7-, and 15-year property the same way in Boston, Cambridge, or Portsmouth. What changes is the state tax posture. A Massachusetts resident pays a state income tax on top of the federal rate; a New Hampshire resident pays 0%. For a Boston-area professional who buys or relocates to a Seacoast rental, that difference is the quiet advantage — the same federal deduction, with no state layer taking a cut.
Learn more
- What is cost segregation?
- The STR tax exception, explained
- Cost segregation in Boston, MA — the metro just south
- Cost segregation in Cambridge, MA — adjacent Massachusetts page
Cost segregation data for Portsmouth, NH investors
The representative (median) outcome across 50 engine-modeled property scenarios matched to the Portsmouth, NH investor profile. Year-1 savings computed at the metro combined bracket of 40.80%.
Representative scenarios modeled via Cost Seg Smart's proprietary
engine — IRS ATG-aligned methodology, industry-standard 2026 construction cost data base costs,
calibrated metro multipliers. n=50 fixtures matched to
Portsmouth, NH investor profile. Not derived from individual
client returns. Methodology v1.0.0, generated
July 2026 (reproducible seed: portsmouth-nh_v1_2026-05-17).
Year-1 savings computed at 40.80% combined (federal 37% + NIIT 3.8%; this state has no personal income tax, so there is no state-side adjustment). Confirm specifics with your CPA.
Tax law current as of July 2026. Federal: OBBBA restored 100% bonus depreciation under §168(k), permanent for property both acquired and placed in service after January 19, 2025 (property acquired or placed in service on or before that date remains under the prior 40% phase-down); 2026+ stays 100%. State conformity varies; verify with your CPA.
CPA use note: These figures estimate the size of the depreciation deduction. Whether the loss is usable in the current year depends on passive-activity rules, STR material participation, REPS status, entity structure, depreciable basis, and state conformity — your CPA decides how and when it is applied. Specialty and site components (equipment, casework, docks, pools, arenas, tenant improvements, and similar) are only classified when you own them and they are included in the depreciable basis being studied.
How should Portsmouth, NH investors choose a cost segregation provider?
For a Portsmouth, NH investor buying a property in the $690,000 range, the choice of study provider is the single biggest controllable variable in the ROI. The methodology is fixed by IRS Audit Techniques Guide rules (industry-standard construction cost data, MACRS classification, engineering-based component reclassification) — what varies is delivery cost and turnaround time.
Traditional engineering studies often run several thousand dollars and can take several weeks, because they include on-site inspections, sales discovery calls, and scheduling overhead. The IRS Cost Segregation Audit Techniques Guide does not require a physical site visit; it requires engineering-based classification with industry-calibrated cost derivation and component-level documentation.
Modern automated providers (such as Cost Seg Smart) deliver the same IRS ATG–aligned study for $495–$1,595 in under one hour, using satellite imagery, county assessor data, and the same industry-standard construction cost databases. For a Portsmouth, NH investor at the metro's combined bracket, that cost delta typically exceeds the study cost itself by several times over. The CPA-Ready Guarantee (full refund if the report can't be used by your CPA) plus the 60-day money-back policy makes the decision essentially risk-free on the report itself.
The automated path is best-fit for Portsmouth, NH investors who: own residential STR property valued under $2M, are comfortable uploading closing docs + property photos online (no in-person visit required), and want the report in time to file the current year's return rather than the next one.
All Cost Seg Smart studies include the CPA-Ready Guarantee (full refund if your CPA can't use the report) plus a 60-day money-back policy. Reports are delivered in under one hour with no on-site visit required.