Best Cost Segregation Software for Short-Term Rentals (2026)

Bonus depreciation is back to 100% — permanently. The One Big Beautiful Bill Act (OBBBA), signed into law on July 4, 2025, permanently restored 100% first-year bonus depreciation under IRC §168(k) for qualifying property acquired and placed in service on or after January 19, 2025. There is no phase-down and no sunset — a clean reversal of the TCJA-era schedule that had bonus depreciation stepping from 100% down toward 0% between 2023 and 2027. IRS Notice 2026-11 (released January 14, 2026) confirmed the operational rules for the new permanent regime. For short-term rental investors, the practical translation is simple: every dollar you reclassify into 5-year personal property or 15-year land improvements — through a cost segregation study — can be written off in Year 1, permanently. (See our full walk-through of the cost segregation vs. bonus depreciation mechanics for how the two work together.)

That reset puts the pressure back on picking the right tool for the right moment. Google "cost segregation calculator" and you'll see the same three sponsored results every time: Cost Seg EZ, Cost Segregation Guys, and FreeCostSeg (Modern CFO). Each one leads with a free tool and monetizes with a paid study behind it. This guide compares those three head-to-head, walks through the most price-competitive paid study on the market (FreeCostSeg's $1,800 flat-rate single-family study), and shows where DepreciMax fits — because DepreciMax solves a fundamentally different problem than any of them: how to use §168(k) before closing, when you're still choosing which property to buy.

Quick comparison

On pricing: Ranges shown reflect vendor-published pricing and industry-typical ranges as of the update date above. Individual quotes vary by property complexity, size, and state; always get a written quote before assuming a figure applies to your situation.

The three free calculators, in detail

1. Cost Seg EZ — Free Estimate (costsegez.com)

Cost Seg EZ leads their Google ad with "DIY Cost Seg Software" and "Get Your Free Estimate Today." Their site pitches a "2-minute" estimate flow, with the calculator front-ending their paid study service.

Strengths. Genuinely fast intake — the ~2-minute pitch from their own marketing is realistic for a directional first look. Refreshingly STR-forward positioning: their landing pages speak directly to Airbnb and Vrbo owners rather than the generic commercial audience most cost seg firms lead with. Established firm behind the tool, so the paid study on the other end of the funnel is a real, credentialed offering — not a bait-and-switch.

Weaknesses. The estimate flow serves as lead-gen for the paid study, so expect sales follow-up. Single-property, single-session shape; no built-in way to compare candidate properties side-by-side before an offer.

2. Cost Segregation Guys — Free Proposal (costsegregationguys.com)

Their Google ad reads "5 Minutes Cost Segregation — No-Cost Tax Savings Analysis." Read carefully: the "5 minutes" refers to how long the intake form takes you. The actual deliverable is a "free proposal in 5 hours" — a rep-generated estimated first-year savings figure and flat quote for the paid study, sent to you by email after their team reviews your submission. There is an on-page illustrative slider, but the real number comes from staff review, not an instant calculator.

Strengths. Rep-reviewed rather than pure algorithm — a real human looks at your property details before you get a number, which catches obvious misclassifications a calculator can't. Five-hour turnaround is genuinely fast for anything with human review in the loop. Fully virtual with no on-site visit required, which is a real convenience for investors buying out-of-state STRs. Broad property-type coverage (single-family, multifamily, commercial), and pricing on the paid side is transparent and flat-fee — no contingency-based pricing, which aligns with the IRS's preferred engagement structure and is a genuine trust marker in this category. Their blog also has some of the most detailed public pricing transparency of any firm in the space.

Weaknesses. Not self-serve — the intake form requires name, email, phone, and property type before you get anything back, and results are delivered by a rep within 5 hours (not instantly). Their paid full studies run $2,000–$4,500 for single-family and scale up sharply from there.

3. FreeCostSeg (Modern CFO) — Free Calculator (freecostseg.com)

Google ad tagline: "Results in 30 Seconds — Lowest engineer-based cost seg fee. Flat rate, no hidden costs, lifetime IRS defense." The free calculator front-ends a genuinely differentiated paid product — the $1,800 flat-rate SFR study covered in the next section.

Strengths. Transparent pricing on the paid study — you can see the $1,800 SFR figure before you submit anything, which is unusual in a category that usually gates pricing behind a sales call. "Lifetime IRS defense" is bundled into the paid product, which is a genuinely strong trust marker most competitors either don't offer or charge extra for. Their AI-native workflow (property records, satellite imagery, construction-cost databases, plus owner-submitted photos → engineer review) is what lets them price the study at roughly half of traditional engineering-firm rates without dropping the engineer sign-off. Deep educational content on their blog — a good signal that the team behind the tool actually understands the space rather than treating it as a generic tax product.

Weaknesses. Contact info (address, name, email, phone) required before you get anything back, and turnaround is typically about a week rather than instant. Free-tier deliverable is an estimated benefit range and flat-fee quote — not a property-specific, component-level breakdown. Single-property tool, so no way to compare candidate homes side-by-side pre-offer.

The paid competitor: FreeCostSeg's $1,800 flat-rate SFR study

Of the paid options one click behind the free calculators, FreeCostSeg's $1,800 single-family flat rate is the most price-competitive engineer-signed study on the market right now. For context, Cost Segregation Guys' comparable single-family study lands at $2,000–$4,500, and traditional engineering firms typically charge $5,000–$15,000 for residential.

How the $1,800 study works. AI-assisted data collection (property records, satellite imagery, construction-cost databases, owner-submitted photos). A licensed engineer reviews the classification decisions and signs the final report. The deliverable is IRS ATG-compliant and audit-defensible.

When it's the right pick. You've already closed on a single-family short-term rental, the property is straightforward (no major renovation, no unusual outbuildings), and you want the cheapest genuinely-defensible study rather than a calculator estimate.

When it's not. You haven't bought yet — a $1,800 study on a property you don't own tells you nothing about the next candidate. Or the property is complex (large multifamily, mixed-use, heavy renovation), where a traditional engineering firm is still the right call. For a deeper look at how the various price tiers compare in defensibility and turnaround, see our breakdown of cost segregation study pricing in 2026.

The traditional engineering-firm options

Above the software and calculator tier, a set of national tax-specialty firms handle the higher-complexity end of the cost segregation market — larger properties, multifamily, commercial, portfolios, and any situation where a CPA or lender wants a name-brand engineer-signed deliverable with formal audit support. The three below are widely used in the industry and appear consistently in CPA-facing referral lists. Facts summarized from each firm's public materials.

4. KBKG (kbkg.com)

KBKG is a national tax-specialty firm headquartered in Pasadena, California, providing cost segregation studies alongside other specialty tax services (R&D tax credit, §179D energy-efficient buildings deduction, §45L, tangible property review). Their cost segregation offering is engineer-signed and produced by an in-house national engineering team.

Positioning. KBKG serves a large CPA channel — many mid-sized accounting firms rely on KBKG as their referral partner for cost seg work — as well as direct-to-investor engagements. Their public materials emphasize IRS Audit Techniques Guide (ATG) compliance, audit-defense support (which they market as "KBKG Rebuttal Support"), and CPA-facing continuing education content on cost seg methodology.

Where it fits. KBKG is most commonly chosen for higher-value residential rentals ($1M+), multifamily, commercial buildings, and situations where a CPA specifically requests a name-brand engineering firm. Public pricing information is not published — quotes are consultative and typically fall in the $3,000–$10,000+ range for residential based on industry-typical reference points; commercial pricing scales higher with property size and complexity. Pricing that starts higher than software-only tools is a function of the scope: on-site or documentation-based engineering review, licensed engineer sign-off, and ongoing audit support are all included.

5. Cost Segregation Services Inc. (CSSI — costsegregationservices.com)

CSSI is a large national cost segregation firm founded in 2001 and headquartered in Louisiana. They publish that they have completed more than 45,000 studies across their history, which — if the number is accurate — puts them among the largest single-firm volume providers in the U.S. cost seg space.

Positioning. CSSI markets primarily through a CPA and financial advisor referral network, with a standardized deliverable format and a national engineering team. Their public materials emphasize scale, methodology consistency across a large study base, and IRS Section 481(a) change-in-accounting-method support for older properties (helpful when catching up depreciation on buildings placed in service in prior years).

Where it fits. CSSI is a common choice when a CPA wants a volume provider with standardized outputs and a national engineer network, particularly for portfolios and for §481(a) catch-up work on properties acquired several years ago. Pricing is consultative rather than published, and industry-typical ranges span from ~$3,000 for straightforward single-family residentials up to $15,000+ for commercial or complex multifamily projects.

6. Cost Seg Smart (costsegsmart.com)

Cost Seg Smart is a self-serve software product in the same category as the free-calculator vendors above, but with a paid deliverable at a lower price point than the traditional engineering firms. The product is DIY-shaped: no on-site engineer inspection, user-supplied property data, and a software-generated report.

Positioning. Public materials position the tool as a low-cost, self-serve alternative for smaller residential rentals where the property is straightforward and the investor is comfortable operating the software directly. Pricing is published on their site and lands in the $495–$2,500 range depending on tier and property type.

Where it fits. Cost Seg Smart competes most directly with FreeCostSeg's paid $1,800 study — both are the software-driven, price-competitive alternatives to engineering-firm studies. The main differentiator is the FreeCostSeg engineer sign-off vs. Cost Seg Smart's software-only deliverable. Whether either is defensible enough for your specific situation is a CPA question — some CPAs are comfortable with software-only outputs on simple SFR rentals; others insist on engineer-signed reports for anything above a certain deduction threshold.

Where DepreciMax fits

DepreciMax solves a different problem than any of the four tools above. Every one of them — free calculator or $1,800 study — assumes you already own (or have under contract) the property in question. They answer: "Given this house, how much can I write off?"

DepreciMax is built for the step before that. You paste an MLS or off-market address, and we return a first-year bonus depreciation estimate — with a land-ratio range, a market bonus-percentage band, and tier context for 197 U.S. short-term rental markets. The core use case is house-hunting: compare five candidate properties in three markets and pick the one that produces the biggest Year-1 write-off before you write the offer. For a walk-through of the pre-offer framework, see how to use §168(k) before closing.

What DepreciMax is.

• An address-based bonus depreciation estimator built on IRS depreciation tables and state Department of Revenue classification data
• Priced at $99 per report for one-off use, $299 for a 10-report Search Pack (the sweet spot for house-hunters actively comparing candidate properties across a market), or $149 / month for Pro (unlimited reports, market alerts, saved workspaces, guide included)
• Buy a single $99 report and decide to upgrade to Pro within 14 days — the $99 credits toward your first Pro month
• 30-day satisfaction-based refund

What DepreciMax is not.

• Not a cost segregation study
• Not IRS-defensible on its own — after you close, you still want a real study (FreeCostSeg's $1,800 product, Cost Seg EZ or Cost Segregation Guys' full study, or a traditional engineering firm depending on property complexity)
• Not a substitute for a licensed CPA's advice on whether you personally qualify for the short-term rental material-participation rules

The honest positioning: use DepreciMax before you buy to pick the right property, then use one of the study tools after you buy to file the deduction.

Who should not use DepreciMax

DepreciMax is the wrong tool for four kinds of buyer. If you're one of them, save the $99 — one of the vendors above will serve you better.

• Long-term rental investors. The whole reason short-term rentals unlock the outsized Year-1 write-off is the seven-day average-stay exception under IRC §469(c)(7) that lets losses offset non-passive income. If your average stay is longer than seven days — traditional annual leases, mid-term corporate rentals, month-to-month — the §469 STR pathway does not apply and the bulk of the tax benefit disappears. You still get depreciation, but at ordinary rental-property speed. Use a full study on the property you close on and skip our pre-purchase estimator entirely.
• Purchases under about $300,000. The Year-1 deduction on a $250K STR is typically $30K–$50K — real money, but our $99 report fee is a bigger fraction of the marginal benefit than it should be. You're better off screening for free on our property search and going straight to a $495–$1,800 study post-close.
• Portfolio investors who need audit-defensible engineering-grade documentation right now. DepreciMax is an estimator built on IRS depreciation tables and state DOR classification data — accurate enough to make a pre-purchase decision, but it is not an engineer-signed study with property-specific site documentation. If your CPA or lender needs the ATG-compliant deliverable today, hire KBKG, R.E. Cost Seg, CSSI, or a comparable firm.
• Anyone needing a formal §168(k) opinion letter for lender or IRS-audit purposes. A pre-purchase estimator is not opinion-grade documentation. Get a full engineering study with a professional-liability-insured engineer's sign-off — that is what a lender or the IRS actually asks for.

When to use cost seg software vs. commission a formal engineered study

The most common question STR investors ask once they've seen the price gap between a $495 self-serve tool and a $10,000 name-brand engineering study is: do I actually need the engineering study, or can the software output stand on its own? The honest answer depends on four variables — none of which are about the software, and all of which are about your specific situation.

1. Size of the Year-1 deduction. The rule of thumb most CPAs use is that the study fee should not exceed roughly 5–10% of the first-year tax savings the study unlocks. On a $250,000 single-family STR producing a $30,000–$50,000 Year-1 write-off, a $2,000 tool is defensible; a $10,000 firm is hard to justify. On a $1.2M luxury vacation home producing a $250,000+ Year-1 write-off, the calculus flips — a $10,000 KBKG or CSSI engagement is well inside the 5% guardrail and buys you the audit support you'd want on a number that size.

2. Property complexity. Straightforward single-family short-term rentals with standard finishes and no unusual outbuildings are the sweet spot for software-only products. Complex properties — luxury vacation homes with detached casitas and pool houses, multi-parcel lakeside compounds with docks and boat lifts, mixed-use buildings, properties with major renovations after purchase — benefit meaningfully from a licensed engineer's on-site or documentation-based review because the classification decisions are more consequential and more contested.

3. Lender or CPA requirements. Some CPAs will file returns based on software-only cost seg outputs; others require engineer-signed studies. Some lenders — particularly for portfolio loans and DSCR products — ask for the formal study as part of underwriting. Ask both your CPA and (if applicable) your lender what they need before spending on either category of tool. This one conversation avoids buying the wrong product twice.

4. Audit exposure and risk tolerance. Bonus depreciation is a well-established IRS provision, but the specific classification decisions in a cost seg study are the highest-audit-risk part of most STR investor returns. Engineer-signed studies with formal audit support (KBKG, CSSI, and comparable firms) come with post-filing defense — if the IRS challenges a classification, the firm defends it. Software-only outputs generally don't include that support. If audit anxiety keeps you up at night, or if you're deducting six-figure amounts, the engineer-signed path pays for itself the first time it matters.

The short version: on a $250K–$500K SFR with straightforward finishes and a CPA comfortable with software outputs, a $1,800 FreeCostSeg study or a $495–$2,500 Cost Seg Smart study is a defensible choice. On anything larger, more complex, or on any property where your CPA or lender specifically wants a name-brand engineer-signed deliverable, the traditional engineering firms are worth the higher price point. Both categories serve real needs.

When to use which

The two stages don't compete — they stack. A $99 pre-purchase report and a $1,800 post-close study are complementary tools for two different moments in the buying process. Trying to use one tool for both jobs is where investors either overpay (commissioning a $7,500 study on a property that doesn't end up closing) or underprepare (skipping the tax analysis at the offer stage and hoping the deduction lands where you thought it would). For a longer look at the difference between free-tool estimates and formal studies, see free calculator vs. $99 AI vs. $5,000 formal study.

Frequently Asked Questions

Sources & further reading

Primary IRS and tax-authority documentation underlying the OBBBA rules and cost segregation guidance cited in this article:

• IRS Notice 2026-11 (interim guidance on OBBBA bonus depreciation): irs.gov/pub/irs-drop/n-26-11.pdf (PDF)
• IRS Newsroom — Treasury/IRS guidance on the additional first-year depreciation deduction under the One, Big, Beautiful Bill: irs.gov newsroom announcement
• IRS Publication 946 — How to Depreciate Property (2025): irs.gov/publications/p946
• IRS — Additional First Year Depreciation Deduction (Bonus) FAQ: irs.gov bonus depreciation FAQ
• RSM US — Restored 100% Bonus Depreciation: IRS Interim Guidance on OBBBA Rules: rsmus.com tax alert
• BDO — One Big Beautiful Bill Act Expands 100% Depreciation Expensing Opportunities: bdo.com analysis
• Moss Adams — Tax Law Reinstates 100% Bonus Depreciation, Reversing Phase-Down: mossadams.com analysis
• Thomson Reuters Tax & Accounting — IRS Provides Guidance on Post-OBBB Bonus Depreciation: tax.thomsonreuters.com

Product names, pricing, and feature descriptions for competing tools were current as of the publish date and were sourced from each vendor's public website. Nothing in this article is tax or legal advice — confirm your situation with a licensed CPA before filing.