You Can Underwrite a Short-Term Rental in Under 60 Seconds. Here's How.
Most aspiring short-term rental investors never buy their first property. Not because they can't find deals. Not because they don't have the capital. Because the underwriting spreadsheet scares them into paralysis.
If you've ever opened a rental analysis sheet, seen rows of formulas, and quietly closed the tab: this is for you. The truth is, you only touch a handful of cells. Everything else calculates itself.
The Spreadsheet Has Five Sections. You Only Control Two.
A standard STR underwriting sheet breaks into five parts:
- Purchasing details: purchase price, down payment percentage, interest rate, amortization, closing costs.
- Renovation and setup costs: your budget for furniture, design, amenities (hot tubs, game rooms, etc.).
- Operating expenses: cleaning, utilities, insurance, property taxes, reserves.
- Revenue forecast: your low, mid, and high revenue projections.
- Results: net operating income, debt service, free cash flow, cash-on-cash return, principal paydown, appreciation, total return.
Section five is all formulas. You never type there. Sections one through four are where you plug in real numbers, and most of those numbers you already know from your earlier research.
Start With the Purchase Details
Enter your purchase price. A $750,000 property at 20% down means a $600,000 loan. Plug in your interest rate (say 7.5%), leave the amortization at 30 years, and estimate closing costs at 2-3%.
That's five fields. You've already started.
Add Your Renovation and Setup Budget
This is where you estimate what it takes to get the property guest-ready. Be specific. A hot tub isn't $7,500. It's $10,000 once you add the electrician, the concrete pad, and delivery. A game room isn't a pool table and an arcade machine. It's installation, setup, and the accessories that make it photograph well.
The sheet totals these line items and adds them to your down payment and closing costs to produce one number: total out of pocket. This is every dollar leaving your bank account before a single guest books.
Plug In Your Revenue Forecast
If you've already built your buy box and run revenue comps (and you should have before you reach this step), you'll have three numbers: a low, mid, and high annual revenue estimate.
Enter those three numbers. The sheet does the rest: calculating your operating expenses as a percentage, subtracting your property management fee (if applicable), removing your mortgage payment, and landing on your free cash flow for each scenario.
STRProfitMap's Property Analyzer generates revenue estimates at four percentile bands (P25 through P90) based on comparable listings in your market.
What the Results Actually Tell You
Free cash flow is your profit. Revenue minus all expenses minus your mortgage. If your total out of pocket was $196,000 and your annual free cash flow is $4,331, that's real money back in your account.
Cash-on-cash return is that free cash flow divided by your total out of pocket. In the example above, that's 2.2%. Simple division, no mystery.
The Property Analyzer calculates NOI, Cap Rate, Cash-on-Cash, and DSCR automatically with color-coded health indicators.
But cash-on-cash isn't your whole return. Your total return combines three things: free cash flow (profit), principal paydown (equity you're building with each mortgage payment), and appreciation (the property gaining value over time).
Most investors obsess over cash flow and ignore the other two. That's a mistake. In year one of a $550,000 property at 3.5% appreciation, you're gaining roughly $19,000 in property value alone. Add principal paydown and even modest cash flow, and your total return could land between 14% and 27%.
The Only Rule: Use Real Numbers
The spreadsheet is only as good as what you feed it. Guess at your cleaning costs and you'll get a fantasy return. Call three cleaning companies in your target market and you'll get a number you can trust.
A detailed expense breakdown keeps your underwriting honest. Every line item matters.
That discipline, real inputs producing realistic outputs, is what separates investors who buy confidently from investors who stare at spreadsheets and never move.
Run Your First Property Analysis Free at STRProfitMap. Enter any address, get revenue estimates, financial metrics, and comparable listings in seconds.
