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5SECONDMODEL COMMERCIAL REAL ESTATE UNDERWRITING

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Back-of-the-napkin commercial real estate underwriting, in seconds.

5 Second Model · back-of-the-napkin underwriting

 

 

 

Rental Property

Residential. Does it cash flow after everything, or does it just look like it does?

This screens a residential rental the way it actually operates: property tax from a millage rate and assessed value rather than a guess, insurance, vacancy, maintenance, management and the mortgage. It reports monthly cash flow, cash-on-cash, cap rate, DSCR and the rent at which you break even, then projects the hold with rent and expense growth running at different rates — because insurance and reassessed taxes have outrun rents in most markets.

Statement of assumptions & returnsAll figures USD · annual unless noted · click any number to type it exactly

Monthly cash flow

--

Where the rent goes, per month

Every dollar of rent, and where it goes

Each line as a share of gross scheduled rent

The screening numbers

Assessed value--
Property tax at that millage--
Cash flow per year--
Net operating income--
Cap rate--
Cash-on-cash return--
Total cash in--
DSCR--
Break-even rent--

If you hold it the full period

Value at exit--
Equity at exit--
Net sale proceeds--
Levered IRR--
Equity multiple--
Net present value--
Expense growth is set above rent growth on purpose. Insurance and reassessed taxes have outrun rents in most markets, and a pro forma that grows both at the same rate quietly manufactures returns. If cash flow is thin today and expenses compound faster than rent, year seven is negative — the projection above will show you the year it turns.
On millage: most assessors quote a millage rate rather than a percentage. One mill is $1 of tax per $1,000 of assessed value, so 12.5 mills is 1.25%. Assessed value is often well below what you paid — some states assess at a fixed ratio, and many reassess on sale, which is the single most common way a rental pro forma turns out wrong in year two.
The 1% rule says monthly rent should be at least 1% of price. It has been near impossible in most US markets since 2021, so treat a miss as a prompt to check the other numbers. The 50% rule says expenses eat about half of gross rent before the mortgage — if you're far under, you probably forgot capex.

Common questions

Does the 1% rule still work?
It has been close to impossible to hit in most US markets since 2021, so treat a miss as a prompt to check the other numbers rather than an automatic pass.
What is the 50% rule?
That operating expenses eat roughly half of gross rent before the mortgage. If your inputs come in far under that, you have probably forgotten capital expenditure.
Why grow expenses faster than rent?
Because they have. A pro forma that grows both at the same rate quietly manufactures returns. If cash flow is thin today and expenses compound faster, the projection will show you the year it turns negative.
Cap Rate Loan Sizing Vacant Retail Box Value-Add Strip Plaza contact@5secondmodel.com New York, NY

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These are screening tools. They round, they assume, and they leave out capital expenditure, income tax, reserves and everything else that matters at the diligence stage. Directionally right is the goal — verify before you sign. Nothing here is investment, tax or legal advice. Every calculation runs in your browser; no data is sent anywhere. © 2026 5 Second Model · New York, NY.