How to Analyze a Rental Deal in 15 Minutes

Most bad rental purchases don't fail because of some hidden defect. They fail because the buyer never actually ran the numbers — they trusted a listing's projected rent, ignored vacancy, forgot capital expenditures, and found out the real cash flow number three months after closing.

This guide walks through the same worksheet used in the rental cash flow calculator, in the order you should actually think through it. Have a specific property in mind, or use the numbers below as a working example.

01Start with the purchase price and financing, not the rent

Everything downstream depends on the loan. Before you touch rent or expenses, lock in four numbers:

• Purchase price
• Down payment percentage — 20–25% is typical for a conventional investment property loan, though DSCR and portfolio loans have their own structures (see our investment property financing guide)
• Interest rate — get a real quote, not a rate you saw in a headline
• Loan term — almost always 30 years for a standard investment mortgage, but confirm it

From those four, the loan amount and monthly principal & interest (P&I) payment fall out of a standard amortization formula. This is not an estimate — it's exact math, and it's the single biggest line item in your expenses.

Input	Example
Purchase price	$239,000
Down payment	25% ($59,750)
Loan amount	$179,250
Interest rate	6.875%
Term	30 years
Monthly P&I	$1,177.54

02Convert advertised rent into effective rent

The rent a listing advertises is gross rent — what the unit collects if it's occupied 100% of the time, forever. No property is occupied 100% of the time forever.

Apply a vacancy assumption before that rent touches any other calculation:

Effective rent = Gross rent × (1 − vacancy %)

A vacancy assumption of 5–8% is a common starting point for a single-family rental in a normal market — it roughly accounts for a couple of weeks of vacancy during a typical tenant turnover, spread across the year. Markets with faster or slower turnover, or with more seasonal demand, can reasonably use a different number; the point is to use some number rather than assuming zero.

On our example: $2,350 gross rent × (1 − 6%) = $2,209 effective rent.

03List every real operating expense — not just the obvious ones

This is where sellers' numbers go wrong most often, usually not through dishonesty but through omission. A seller who has owned a property for fifteen years may genuinely not remember the last time they paid for a water heater.

Build the expense list yourself:

• Property tax and insurance (get real quotes — don't reuse the seller's, which may reflect a different insurance history or a homestead exemption you won't qualify for)
• HOA fees, if any
• Property management, if you won't self-manage (commonly 8–10% of collected rent)
• Maintenance reserve — a monthly amount set aside for the ordinary wear of owning a building, separate from big-ticket capital expenditures
• Capital expenditure reserve — a separate monthly amount set aside for roof, HVAC, water heater, and other large replacements that happen every several years, not every month

A monthly expense figure that excludes maintenance and cap-ex reserves isn't conservative — it's incomplete. Those costs are certain to happen eventually; the only question is when.

04Calculate monthly cash flow

With effective rent, the P&I payment, and total monthly expenses in hand, cash flow is simple subtraction:

Monthly cash flow = Effective rent − P&I − monthly expenses

$2,209 − $1,177.54 − $610 = $421.46/month

This is the number that determines whether the property pays you or costs you every month it's occupied at your assumed vacancy rate.

05Check cash-on-cash return

Cash flow alone doesn't tell you whether the deal was worth the capital it took to get there. Cash-on-cash return answers that by dividing the cash flow you'll actually collect by the cash you actually put in:

Cash invested = Down payment + closing costs
Cash-on-cash return = (Monthly cash flow × 12) ÷ cash invested

On the example: down payment $59,750 + closing costs (3%, $7,170) = $66,920 invested. Annual cash flow of $5,057.52 ÷ $66,920 = 7.56% cash-on-cash return.

See the full cash-on-cash return guide for how to read this number and what a reasonable target looks like.

06Check cap rate

Cap rate strips financing out entirely and asks: if you paid all cash, what would this property yield?

NOI = (Effective rent − monthly expenses) × 12
Cap rate = NOI ÷ purchase price

NOI here is $1,599/month × 12 = $19,188. Cap rate = $19,188 ÷ $239,000 = 8.03%.

Cap rate is the fastest way to compare two properties at different price points, because it removes your specific loan terms from the equation. See the cap rate guide for a full breakdown.

07Grade the deal against a benchmark — and let it floor, not round

A single metric rarely tells the whole story. This site's calculators check a deal against three benchmarks at once — cash flow, cash-on-cash return, and cap rate — and grade it based on how many it actually clears:

• Clears all three → A
• Clears two of three → B
• Clears one of three → C
• Clears none → D
• Negative cash flow → F, regardless of the other two

Two out of three benchmarks passed is a B, not an A rounded up. That's deliberate — a calculator that's generous with grades isn't doing you any favors before you sign a contract.

Run the exact numbers from this walkthrough in the rental cash flow calculator to see the grade and benchmark rails for yourself, or plug in your own deal.

08What this worksheet doesn't cover

This is a cash-flow underwriting worksheet, not a complete investment thesis. It doesn't account for:

• Expected appreciation or equity growth, which some investors weigh heavily and others ignore entirely
• Tax treatment (depreciation, 1031 exchanges) — see our tax-adjacent guides for how those work
• Neighborhood trajectory, school zones, or other qualitative factors a spreadsheet can't capture
• Your own risk tolerance and how a vacancy or a large repair would actually affect your finances

Use this worksheet to rule out deals that don't clear a basic bar, and to make an informed offer on the ones that do — not as the only diligence you do. See our property due diligence guide for the rest of the checklist.