What a cash flow forecast adds
An underwriting model tells you whether a deal might work on an annual basis. A cash flow forecast shows the monthly timing, so you can see slow months, lump-sum bills, and whether your reserves are adequate. It is also the tool you use after purchase to compare plan with actual results.
Step 1: Set up the structure
Build a spreadsheet with months across the top (12 columns, plus a total) and line items down the side, in this order:
- Revenue
- Variable operating costs
- Fixed operating costs
- Net operating income
- Debt service
- Reserve contributions
- Net cash flow
- Ending cash balance
Step 2: Forecast revenue by month
Use ADR, occupancy, and days in each month (see revenue management basics and seasonality planning). Include a ramp-up for a new listing: first months at lower occupancy while reviews build.
Formula: Monthly revenue = ADR x occupancy x days in month.
Example (illustrative only): July with ADR $320, occupancy 70 percent, 31 days: $320 x 0.70 x 31 = $6,944. February with ADR $240, occupancy 40 percent, 28 days: $240 x 0.40 x 28 = $2,688.
Step 3: Separate variable and fixed costs
Variable costs move with bookings: cleaning, laundry, supplies, platform fees, management percentage, and occupancy taxes collected (track them as pass-through, not income; see occupancy tax basics).
Fixed costs do not: utilities, internet, insurance, software, property tax, HOA, and lawn or pool service. Include costs that arrive as lump sums, such as an annual insurance premium or a semiannual tax bill, in the month they are actually paid, or set aside monthly.
Step 4: Add debt service and reserves
Enter the mortgage payment monthly. Add a monthly transfer to the maintenance reserve (see maintenance reserve planning). Keep the operating cash balance visible.
Step 5: Worked mini-example
Example (illustrative only): Consider two months. In July, revenue is $6,944. Variable costs at 32 percent = $2,222. Fixed costs = $1,400. NOI = $6,944 minus $2,222 minus $1,400 = $3,322. Debt service $2,300 and reserve contribution $350 leave $672 of net cash flow. In February, revenue is $2,688. Variable costs at 32 percent = $860. Fixed costs = $1,400. NOI = $428. Debt service $2,300 and reserve $350 produce net cash flow of negative $2,222. Across the year the property might still be positive, but February shows why you need an operating cash cushion. Your numbers will differ.
Step 6: Build three scenarios
- Base: your most reasonable assumptions.
- Conservative: occupancy lower by 10 percentage points, ADR lower by 10 percent, expenses higher by 10 percent.
- Upside: modestly better than base. Do not plan around this one.
Find the lowest ending cash balance in the conservative case. That number is the minimum liquidity you need to hold.
Step 7: Choose a minimum cash trigger
Decide the balance at which you take action, such as cutting discretionary spending, increasing marketing effort, adding mid-term stays in slow periods where allowed, or injecting cash. Write the plan before you need it.
Step 8: Update monthly with actuals
- At each month-end, enter actual revenue and expenses.
- Compute variance by line item, forecast versus actual.
- Note the causes (a price change, a repair, an unexpected cancellation).
- Roll the forecast forward by adjusting the remaining months if patterns change.
- Review a trailing 12-month total once you have enough history.
Tips for accuracy
- Use a separate bank account so property cash flow is clear.
- Categorize expenses consistently so the actuals match your forecast lines.
- Record booking dates by stay month, or by payout month, and stay consistent, because platforms pay after check-in.
- Keep a note on assumptions on the sheet.
Common mistakes
- Forecasting only annual totals
- Forgetting lump-sum costs
- Counting collected lodging tax as revenue
- Omitting a ramp-up period for a new listing
- Not updating with actual numbers
- Building only an optimistic scenario
- Ignoring the timing gap between booking, payout, and expenses
Use the outputs to test ideas from underwriting basics, and revisit them whenever assumptions change.
Connecting the forecast to decisions
A forecast is useful only if it changes what you do. Use it to decide when to schedule big maintenance, when to hold back on discretionary upgrades, and whether to add slow-season strategies. If the conservative case shows a cash shortfall, either raise your reserve, lower your costs, or reconsider the deal.
Monthly review questions
- Which line items missed the forecast by the most?
- Was the miss a one-time event or a pattern?
- Does the lowest projected cash balance still hold?
- Do upcoming lump-sum bills need to be funded now?
Over time, your own history will make forecasts more accurate than any general rule of thumb.
Key takeaways
- Forecast monthly, since annual totals hide slow-month shortfalls.
- Track lump-sum bills in the month they are paid.
- Build a conservative scenario and hold liquidity to match it.
- Update with actual results every month.
Educational only: this guide is general education, not financial advice; all figures are illustrative.