An operating model is the engine behind every forward-looking number: the budget, runway, the hiring plan and the fundraising narrative. A good one is driven by a few assumptions you can defend and is built on the same structure as your books, so actuals drop into it every month.
The structure
| Module | Key drivers |
|---|---|
| Revenue | New ARR by month and segment, expansion and churn rates, pricing changes, billing terms |
| Cost of revenue | Hosting per customer or per unit of usage, support staff per customer, third-party fees |
| Headcount | Role, department, start date, salary, taxes and benefits rate, recruiting cost |
| Non-headcount opex | Software per head, marketing programs, rent, professional fees |
| Cash | Collection timing, annual prepayments, payables timing, capex, taxes, financing |
| Outputs | P&L, balance sheet, cash flow, ARR bridge, burn multiple, runway |
Headcount drives most of it
For most SaaS companies, people are the majority of operating expense. Plan by individual role, not by department totals:
| Role | Department | Start | Salary | Loaded cost per month |
|---|---|---|---|---|
| Account executive | Sales | March | $95,000 | about $10,300 |
| Senior engineer | R&D | April | $185,000 | about $19,700 |
| Support specialist | Cost of revenue | May | $65,000 | about $7,000 |
Loaded cost adds employer taxes, benefits and per-head software. Each role can carry a productivity assumption (for example, a ramped quota for sales hires) that links hiring to revenue.
Tie it to the books
Use the same chart of accounts and departments as the ledger. Each month, replace forecast with actuals for the closed month and roll forward. The variance between last month's forecast and actual is the best feedback on which assumptions need work.
Scenarios
Keep a base case and a downside case at minimum. The downside should change the inputs that actually move: slower new ARR, a large customer churning, hiring delays. Runway in the downside case is the number to plan the next raise around.
Common mistakes
- Revenue growth typed in as a percentage instead of built from bookings and retention.
- Headcount planned as a total cost with no start dates.
- Annual prepayments ignored in the cash flow.
- A model nobody updates after the budget is approved.
Monthly upkeep
After each close: load actuals, review variances by department, update the hiring plan for offers accepted and roles pushed out, and refresh runway in both cases.
We build the model with your leadership team, update it after every close, and use it to produce the reforecast, runway and the numbers for the next board meeting.
Sources
Questions founders ask
How far out should the model go?
Monthly for at least 24 months, which usually covers the runway and the next raise. Annual columns beyond that for long-range scenarios.
Should the model and the budget be the same file?
The approved budget is a frozen version of the model at a point in time. The live model keeps changing as the business does, and becomes the reforecast.
