When I screened listings for my own duplex, the useful shift was realizing I was not hunting for a winner. I was eliminating losers as cheaply as possible. Every pass below costs more time or money than the one before it, so the order is the method: kill bad deals with free checks before you spend an afternoon, or an inspection fee, on a building that was never going to work.
Pass one: the metro sets your ceiling
No amount of good shopping fixes a metro where typical rents cover a thin slice of typical payments. Before looking at a single listing, check the ratio of rent to price where you are searching.
I publish my own version of this math as the Foothold Score, which ranks metros by how far a two-unit building’s rent goes against its costs, but the principle works anywhere: if typical unit rent times two falls far short of the typical all-in payment, the metro fails the pass and the listings inside it inherit the failure.
Pass two: the block, not the zip code
Averages lie at the neighborhood level. Walk the block on a weekday evening and answer two questions. Would the tenants who have options choose this street? And what is already vacant here? Boarded windows two doors down matter more than any citywide statistic.
My rule for an owner-occupied building is blunt: I am going to live in one unit, so if I would not live there, I assume tenants with choices will not either, and the rent the listing promises is fiction.
Pass three: the five expensive systems
Cosmetic ugliness is a discount. Structural and mechanical problems are a second mortgage. Before paying for anything, stand in front of the building and price five things:
the roof, the heating plant, the electrical panels, the plumbing stack, and the foundation. On a 2-4 unit building, also count meters. Separate gas and electric meters mean tenants can pay their own utilities; a single meter means you are buying everyone’s hot showers forever. None of this replaces a professional inspection. It decides whether the building has earned one.
Pass four: the month the numbers hate you
Every listing pencils out in the month nothing breaks and everyone pays. That month is not the test. Whatever your quoted rate and payment turn out to be, re-run the deal three ways.
- With one unit empty for two months of the year.
- With repairs at one percent of the purchase price per year.
- With rents ten percent under the listing’s claim.
A deal that survives all three is a deal. A deal that only works in the sunny version is a hope with a mortgage attached.
The arithmetic itself is the easy part: cash flow, cap rate and the 1% rule each get their own explainer on this site, and the Deal Screener runs the four quick checks on any building in about a minute.
Why the order matters
The metro pass costs nothing and kills whole search areas. The block pass costs an evening. The systems pass costs a hard look and maybe a contractor’s opinion. Only the survivors deserve the inspection fee and the full spreadsheet. Analysis done in this order is boring, and boring is the point: by the time you are paying anyone, the building has already passed everything a careful stranger could check for free.
Run a specific building through the four passes.
The free house hacking calculator. Enter a price, a rent and your loan terms, and it returns cash flow, cash-on-cash and your effective housing cost in one pass.
What is the first thing to check when analyzing a 2-4 unit property?
The metro, not the listing. If typical unit rents in the area cover only a thin slice of a typical all-in monthly payment, no individual building fixes that math. Check the market level first, then judge specific properties.
What is a stress test in rental property analysis?
Re-running the numbers on a bad year instead of a perfect one: one unit empty for two months, repairs at about one percent of the purchase price for the year, and rents ten percent below what the listing claims. A deal that survives all three is worth pursuing.
Do I need a professional inspection for a duplex?
Yes, but only after the building has passed the free checks. The inspection’s job is to price the five expensive systems: roof, heating, electrical panels, plumbing stack, and foundation. Spending that money on a building that already failed the cheap screens is how analysis gets expensive.
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Sources
The expense ratios and vacancy assumptions used here are planning estimates rather than market data. Property taxes, insurance and utility costs vary by county and by building; pull the recorded figures for any property you analyze.