Underwriting the Expense Stack

There are two profit-and-loss statements for every rental: the one in the listing and the one you'll live with. The listing's version isn't a lie. It's the seller's history in numbers: their tax bill, their insurance, their deferred repairs, their free labor. Yours starts with a different set of costs. If the math changes the deal, it's better to know before the offer than after closing.

This chapter prices that gap, cost by cost, in the order those expenses tend to ambush people: insurance, taxes, vacancy, capital reserves, HOA, management. Then we run the duplex from Chapter 2, Buy Box Before You Shop two ways: first with the brochure's numbers, then with the real stack. Same property, two different stories.

The two P&Ls

Sellers quote what the property cost them. Buyers have to price what comes next. That's structural, not dishonest. A long-time owner carries a tax assessment from their purchase price, an insurance policy priced years ago, systems they've stopped maintaining, and management they do themselves on Saturdays. Those numbers belong to their ownership. Yours need to be built for yours.

The real work starts with your own expense stack: your purchase price, today's quotes, and assumptions built for your ownership. The listing is a reference, not the answer. Line by line, the translation looks like this:

• Their tax bill, based on their old purchase price, becomes your tax bill, modeled from yours.
• Their insurance premium, priced years ago, becomes a fresh quote on today's market.
• Their "low maintenance" becomes your repair reserve, because deferred is not the same as absent.
• Their invisible weekends become your management line, priced whether or not you hire it out.
• Their fully-occupied year becomes your market's actual vacancy rate.

The rest of the chapter reveals what happens to those numbers once the property changes hands.

Insurance before the offer

Insurance is one of the fastest ways for a good-looking deal to change shape. The seller may be paying a premium set years ago. You won't be. The average U.S. home policy ran $2,948 in 2025 after a 12% jump in one year, is projected at $3,057 for 2026, and has climbed 46% since 2021. Florida's average is $8,292, nearly three times the national figure.¹ In places where carriers are pulling back, the problem is bigger than price. More disaster-exposed properties are landing in state-backed insurers of last resort. California's FAIR Plan reported 696,562 policies in force as of June 2026, up 157% since September 2022.² The insurance market is telling you something about the property. Listen before you own it.

The rule here is straightforward: get a bindable quote on the actual address before the offer. A rate survey is background. Last year's premium is history. What matters is the number attached to this property, under this ownership, as a rental. Come prepared with the address, year built, roof age and material, construction type, entity name if you're vesting in one, and intended use. Be clear that the property will be used as a rental. An owner-occupied quote may come in lower, but it won't reflect the real cost of rental coverage. While the quote is coming together, check three things:

1. Make sure it is actually a landlord policy. A homeowner's policy is built for owner occupancy. A rental needs coverage written for a rental, with a price to match.
2. Look closely at the wind and hail deductible. In many markets, it is a percentage of the dwelling coverage rather than a flat amount. That can turn "covered" into a five-figure check before the policy pays. Convert the percentage to dollars. Percentages tend to look a little friendlier before you do the math.
3. Check the flood determination. Flood is separate coverage, lenders may require it in mapped zones, and your buy box already told you whether unconfirmed flood exposure ends the conversation.

If carriers hesitate to quote the address, that belongs in the underwriting too. Trouble getting coverage is an added weight on the deal. The quote you get here is the one you expect to bind before closing, and it is the first row on the toolkit's Pre-Offer Checklist. Chapter 5, Close and the First 90 Days picks up from there.

The tax bill resets when you buy

The seller's tax bill reflects their ownership history. Yours will reflect yours. This is the trap behind the reject-on-sight signal from Chapter 2: the listing whose taxes look wonderfully low next to the neighbors'. Low often means owned a long time, and that discount usually dies with the sale.

Two states in our footprint show how it works. The same three questions matter in both: what happens when the property sells, what happens to any cap, and when the new assessment takes effect.

Florida. When the property sells, the assessment resets to full market value.³ The 10% annual cap that limited increases for the previous owner resets with it. Their protection does not transfer to you. The reset takes effect January 1 after the sale, so a June purchase can show up at the new value on the next tax roll.

Texas. The same basic reset happens when the property sells, with one twist worth knowing. Non-homestead property currently has a 20% annual cap on appraised-value increases, but that protection does not follow the property to the new owner.⁴ The cap itself is temporary too. It's a pilot covering tax years 2024 through 2026 unless the legislature extends it. A Texas buyer today shouldn't underwrite as though that protection will be waiting on the other side of closing.

Tennessee adds a question the first two don't ask: which class the property falls into. The state assesses residential property at 25% of its value and commercial property at 40%, and its constitution defines residential property with two or more rental units as commercial.⁵ A duplex held as a rental is assessed at the commercial ratio, 60% more than the single-family next door. If the seller lived in one unit, the listing's tax bill may reflect a classification your ownership won't get.

The rule that survives every state's mechanics: model the tax line from your purchase price, the local rate, and the classification your use will trigger, never from the listing. Your county appraiser's site publishes the rate and the classes. Run the number before you offer, and if the modeled bill breaks the deal, the listing's tax bill was never going to save it.

Vacancy at the market's actual rate

Every pro forma assumes 5% vacancy. The market doesn't. The national rental vacancy rate runs 7.3%, and the South, where much of the investor pipeline lives, runs 9.5%.⁶ The gap between hoped-for and actual vacancy is roughly one additional vacant month. On the duplex, that means $2,600 of missing income while every expense line keeps arriving on schedule.

Underwrite to the vacancy rate your market is actually carrying, not what's listed. Vacancy isn't just an event in the math. It's a reserve that builds every month so the income lost during a vacant month is already accounted for when it happens. That's how the calculator handles vacancy, and why our numbers tend to run smaller and truer than the listing's. Chapter 1, The Market Read, keeps the current vacancy picture updated each quarter.

Capex is not maintenance

Repairs keep the property running. Capital expenses replace it, one component at a time, and they belong in two different reserves. Maintenance is the leaking faucet and the serviced furnace: smaller, recurring costs. Capital is the roof, the HVAC, the water heater, the flooring: bigger, less frequent, and eventually unavoidable. Every component is a countdown clock that started before you arrived.

The durable way to budget capex is component by component. Start with four steps:

1. List the major components: roof, HVAC, water heater, flooring, and the rest of the big-ticket systems.
2. Note each one's age against its typical service life.
3. Get local replacement quotes for anything in the final third of its life.
4. Fund a monthly reserve sized to those real quotes and timelines.

A property with a young roof and a 20-year-old water heater isn't simply "in great shape." One major expense may be years away, while another could be closing in. The inspection report helps you estimate when those costs are likely to arrive. Price the replacements before the offer. Chapter 2's condition rules already flagged which properties deserve the hardest look. This is where those flags turn into actual numbers.

HOA, the quiet lien

An HOA is a business partner you didn't interview, with the power to bill you. If the property sits in an association, the dues are the only visible cost. The rest shows up in the documents, where the real obligations start to surface. Here's what deserves a closer look:

• the current budget and reserve study, because an underfunded association can lead to future special assessments;
• any pending or recent special assessments;
• rental caps, approval rights, and lease minimums, which can limit the property's rental use and may belong on your disqualifier list;
• the association's insurance, because anything the master policy leaves out still needs to be covered by your own policy.

Condo buyers already know the lender underwrites the building alongside the borrower. Reading the HOA documents means doing the same underwriting for yourself.

Management, honestly

Management is a cost even when nobody sends an invoice. If you hire a professional, use the actual fee in your monthly expenses. If you manage the property yourself, budget what it would cost to replace you. Calls, tenant issues, bookkeeping, and Saturday drives still take time. A deal that only works because your labor is free isn't income. It's a job you bought. Use the going rate even if you plan to do the work yourself, then give the deal one last honesty check: would it still work in a year when you can't give it your Saturdays? Chapter 6, Operating in a Flat-Rent Market, takes a fuller look at self-managing, including when it genuinely wins. For now, make sure the cost is included either way.

This chapter stays with the costs of owning. What ownership does to your income taxes, depreciation included, is a different part of the math, with better news waiting in Chapter 7, The Tax Layer.

The same property, underwritten twice

Now watch the whole stack work. The duplex from Chapter 2 is still sitting at its $300,000 asking price with $2,600 in total monthly rent. Same property, same loan, two sets of assumptions. Both are illustrative, computed from the stated inputs. The brochure stack uses the listing's optimism: 5% vacancy, a hopeful $50 a month for maintenance, no management cost, the seller's $2,350 historical tax bill, and a $1,400 insurance estimate. The real stack uses the same property with this chapter's assumptions: market vacancy, realistic repair reserves, management priced in, and taxes and insurance updated for the purchase.

	Brochure stack	Real stack
Coverage ratio	1.38	1.30
Monthly cash flow	$534	$24
Verdict against the Chapter 2 box	Comfortable everywhere	Covers, but fails the $250 floor at asking; clears it at $265,000

Same address, same rent, same loan. The property didn't change. The assumptions did. The brochure version clears every test and sends you toward an offer. Your version covers the debt and leaves about two dozen dollars a month at asking, which is exactly the number that sent Chapter 2's buyer into a negotiation instead of a purchase. Run the real stack yourself, change any line, and watch which ones move the verdict.

The two questions every chapter answers. On the ratio: the expense stack determines how much income is actually left to cover the debt. On cash flow: every cost you price before the offer is one less surprise waiting after closing.

Numbers above are illustrative scenarios computed by our calculators from the stated inputs. They are not offers, quotes, or records of transactions. OneMoreDoor Capital arranges business-purpose financing for non-owner-occupied investment property through its lending partners.

Footnotes

1. Insurify, 2026 Insuring the American Homeowner Report: 2025 national average $2,948 after a 12% annual increase; 2026 projected at $3,057; premiums up 46% since 2021; Florida average $8,292. ↩

2. California FAIR Plan, Key Statistics & Data: policies in force and growth as of the edition cited; updated quarterly. Chapter 1 carries the live figures and refreshes them each quarter. ↩

3. Florida Statutes 193.155(3)(a) and 193.1554: assessment at just value as of January 1 following a change of ownership; the non-homestead 10% cap resets on transfer. ↩

4. Texas Tax Code 23.231 and the Texas Comptroller: 20% circuit-breaker limitation on non-homestead real property for tax years 2024 through 2026, eligibility capped, expires December 31, 2026 unless extended, and expires for a property on the January 1 after it changes owners. ↩

5. Tennessee Code 67-5-801 and Tennessee Constitution Article II, section 28, codified at Tennessee Code 67-5-501(11) (residential property assessed at 25% of value, industrial and commercial at 40%; residential property containing two or more rental units defined as industrial and commercial); the Comptroller of the Treasury's property assessment glossary. ↩

6. U.S. Census Bureau, Housing Vacancies and Homeownership (CPS/HVS), Q2 2026 release: rental vacancy 7.3% national, 9.5% South; year-over-year change not statistically significant. ↩