Most listings are a no. The skill that compounds in real estate isn't underwriting the one deal you buy — it's saying no to the ninety-nine you don't, quickly, without burning an evening in a spreadsheet for each one. Here is the exact screen we built Mortar around. It takes under a minute per listing once it's muscle memory.
Step 1 — Anchor on price and rent, nothing else yet
Open the listing and write down two numbers: the asking price and the realistic monthly rent. Everything downstream is a function of these two. Don't trust a gut rent figure — pull a real one. Zillow publishes a Rent Zestimate on many listings; that's your starting anchor. If the page doesn't have one, look at what comparable units actually lease for, not what they list for.
The single most common way investors fool themselves is an optimistic rent. A $200/mo rent error flips a marginal deal from a yes to a no. Use a sourced number and label your confidence in it.
Step 2 — Compute the four numbers that matter
You don't need a fifteen-tab model to screen. You need four figures, computed the same way every time:
- Monthly cash flow — rent minus mortgage, taxes, insurance, and realistic reserves (vacancy, maintenance, management). If this is negative on a buy-and-hold, the rest barely matters.
- Cap rate — net operating income divided by price. A capital-structure-free read on the asset itself; lets you compare two properties without financing noise.
- Cash-on-cash return — annual pre-tax cash flow divided by the actual cash you put in. This is the number that answers "what is my money earning here?"
- Gross rent multiplier (GRM) — price divided by annual rent. A five-second sanity check you can do in your head before anything else.
The discipline that matters more than the formulas: use the same assumptions every time. If one deal assumes 5% vacancy and the next assumes zero, you're not comparing properties — you're comparing your moods. Fix your assumptions (down payment, rate, term, vacancy, maintenance, management) and let the property be the only variable.
Step 3 — Use local taxes and insurance, not national averages
This is where most quick calculators quietly lie. Property tax in Texas can run several times a national-average assumption; insurance in coastal Florida is in a different universe than the Midwest. A 1.2% blanket tax assumption makes a Houston fourplex look like a winner that, taxed correctly, bleeds every month. Screen with real per-state (ideally per-county) tax and insurance, or your verdict is fiction in exactly the markets investors care most about.
Step 4 — Read the verdict as triage, not gospel
A fast screen produces one of three outcomes, and all three are useful:
- Pass — the numbers don't work under honest assumptions. Move on; your time is the scarce resource.
- Investigate — close enough that a real underwrite, a rehab estimate, or a rent push could tip it. Worth an hour.
- Pursue — clears your thresholds with margin. Now you open the spreadsheet and verify everything.
A screen is a filter, not an appraisal. Its job is to protect your attention, then hand the survivors to a deeper process.
Step 5 — Score it against your box, not a generic rule
"Is a 6% cap good?" has no answer in the abstract. It depends on your market, your strategy, and your minimum cash flow. The last step of a fast screen is comparing the deal to your buy box — your target markets, your strategy, your floors — so the verdict is personal. A deal that's a clear pass for an out-of-state turnkey buyer can be a clear pursue for a local BRRRR operator looking at the same listing.
This is the entire reason Mortar exists: run this five-step screen automatically, on the listing you already have open, scored against your box, in the time it takes to read the address. Estimates only — always verify before you offer.