Gross booking revenue is only the top line. A defensible STR model names each cost, says whether it changes with bookings, and shows who pays it. Missing even modest recurring items can turn projected cash flow into a loss.
Separate operating costs from financing
Operating costs typically include property tax, insurance, utilities, internet, platform fees, management or co-host fees, software, cleaning net of guest cleaning fees, laundry, supplies, lawn or pool care, pest control, licenses, accounting, repairs, and routine maintenance. Add HOA dues where applicable.
Net operating income is revenue minus operating expenses, before debt service. Cash flow then subtracts principal and interest payments and any other financing costs. Keeping these lines separate lets you compare properties with different loans.
Calculate the expense ratio, then inspect the lines
The operating expense ratio is operating expenses divided by gross operating revenue. For example, $32,000 of annual operating costs on $80,000 of revenue is 40%. The ratio excludes debt service; otherwise two identical homes with different loans would appear to operate differently.
Use the ratio as a warning light, not a universal pass mark. Compare each category with bills, bids, and comparable properties. A percentage shortcut hides cleaning frequency, weather-driven utilities, and insurance premiums that vary by property.
Budget for replacements and owner time
Furniture, linens, appliances, hot tubs, and HVAC systems wear out. Set aside a recurring replacement reserve based on the actual asset list and condition rather than treating each failure as a surprise. If you self-manage, count your time or model the cost of hiring a manager so the investment comparison is honest.
Booking-driven costs rise with turns and occupied nights. Fixed costs continue in slow months.
Run three cases
Build a base case from comparable listings or verified seller history, a downside case with lower occupancy and rate, and an upside case with evidence for the improvement. Hold most fixed expenses constant in the downside case. Calculate break-even occupancy and test whether reserves cover a weak season.
Our cash flow analysis guide explains the return metrics to use after the expense model is complete.
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Frequently asked questions
What is the biggest expense in a short-term rental?
It varies. Debt service is often the largest cash outflow, while management, cleaning, property tax, insurance, and utilities are major operating lines. Model the actual property rather than using a universal percentage.
Should mortgage payments be included in NOI?
No. Net operating income excludes financing. Subtract debt service after NOI to calculate cash flow to the owner.