What do you double check before trusting the numbers on a rental deal?

Question

I've been learning more about how people analyze rental deals, and I'm curious what you guys do after you've run the numbers.

Whether you use a spreadsheet, the BiggerPockets calculator, DealCheck, or something else, what numbers do you usually double-check before you feel comfortable with a deal?

Rents, taxes, insurance, repairs, financing, comps, or something else?

And how do you usually verify them?

Just trying to understand what that process actually looks like before you decide the numbers are solid enough to move forward.

Benjamin Voorhees · Answer

Good question — and honestly the verification step is where most beginners skip corners and pay for it later.

Here's the process I'd recommend and what I see experienced investors actually do:

Rents — never trust the listing.
Pull comps yourself on Zillow, Rentometer, and Facebook Marketplace. Call 2–3 property managers in that zip code and ask what a property like this would actually rent for right now. Property managers have no incentive to inflate that number — they're your most honest source.

Taxes — always look up the actual current bill AND call the county.
What's listed online is often last year's assessment. More importantly — ask whether the property will be reassessed after purchase. In many counties the tax bill jumps 30–50% after a sale. That can completely change your cash flow calculation.

Insurance — get an actual quote before you close.
Don't estimate. Call an insurance agent with the address and property details and get a real number. Flood zone, roof age, and property class all affect this more than most people expect.

Repairs & CapEx — this is where most new investors get humbled.
Look up the age of the roof, HVAC, water heater, and electrical. Budget for replacement on anything over 10 years old even if it's currently working. I use 10% of monthly rent for maintenance and another 5–10% for CapEx reserves — separately from each other.

Financing — model the actual payment, not an estimate.
Get a real rate quote from your lender before you underwrite the deal. Rates shift and a half point difference can turn a cash flowing deal into a breakeven one.

Comps — pull them yourself, don't rely on automated values.
Half mile radius, same bed/bath, same square footage range, sold in the last 90 days. If you can't find clean comps — that's important information too.

The one number most people forget — vacancy.
Budget 8–10% vacancy even in strong markets. That's roughly one month per year the unit sits empty between tenants. If your deal only works with 100% occupancy all year — it doesn't work.

Run all of that. If it still cash flows — you probably have a real deal. 💪

Happy to answer any questions on the financing side of the analysis if it comes up. 🤝

Patrick Parry · Answer

I’d start with the numbers that can change the deal the fastest. Rent is a big one, so I’d compare it against recent nearby rentals instead of trusting the listing estimate. For the other major costs, I’d rather work from actual bills, quotes or current loan terms than rough assumptions.

After that, I’d see how the deal holds up with more conservative assumptions. Drop the rent a little and raise the expenses. If it still works without everything going perfectly, I’d feel much better about the numbers.

Garth Huxtable · Answer

@Alyssa Marquez

I like your take on not just going with one rent estimate.When you’re checking out a few different rentals, what do you usually look for to decide if an estimate feels right? Are there certain things about the other places that you pay extra attention to?

Garth Huxtable · Answer

@Benjamin Voorhees

Thanks for breaking down your process! It sounds like you pull info from a bunch of different places before feeling good about the numbers.Out of all those checks, is there one that usually gives you the most grief or takes the longest? Or is hopping between different sources just part of the groove for you now?

Garth Huxtable · Answer

@Michael K GallagherYour point about needing to understand the reasoning behind a number and being able to back it up totally makes sense.What do you usually do when the info you're looking at doesn’t match up? Like, if different sources are giving you different rental prices or expense estimates, how do you figure out which number you’re cool with for underwriting?

Garth Huxtable · Answer

@G. Brian Davis

That point about spending more time questioning the numbers instead of just running them really hit home for me.Out of all the numbers you look at, which one usually takes the most work before you feel like it’s spot on? What makes that one tougher to verify than the rest?

Michael K Gallagher · Answer

might be an unpopular opinion, but "analizing a deal" is way more art and black magic than most people let on.  Sure on the surface its just math, but if you are projecting numbers and expenses its really just an edgucated guess and to your question, its not the numbers but "being confident" in them, and that just takes operating unfortunatley.  you can of course get close, and things like taxes, ins, etc are fixed, but even the entire appraisal process is way more subjective than people think at first.  but to your point, I think as long as you can track the logic of the number, or "defend it" in a manor of speaking then that's really as good as you can expect to be unless you are dealing with real operational data.  and in small buildings and single families those records rarely exist or oare accurate.

G. Brian Davis · Answer

I probably spend more time questioning the numbers than running them. Anyone can put numbers into a calculator, but the hard part is knowing if those numbers are realistic. I want to know what similar properties are actually renting for, what the real expenses have been, and what I might be missing before I get too excited about a deal. A lot of bad deals look good on paper because one or two assumptions are too optimistic. Maybe the rent is a little high, the repairs are underestimated, or the expenses are lower than they should be. I’d rather be conservative going in and make sure the deal still works if things don’t go exactly as planned.

Alyssa Marquez · Answer

For me, I generally find the three biggest items to confirm to be rents, property taxes, insurance, and financing and the biggest ones because these one items can sway the deal one way or another really fast. Rents should be compared against three other rentals versus picking one quote and should include a vacancy reserve with contingency funds included for general maintenance and repairs. If the deal looks to work out then some conservative numbers are always positive sign.

What do you double check before trusting the numbers on a rental deal?

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