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OPEX covers a wide range of cost lines (software, marketing, facilities, professional services), each with different predictability and drivers. Salaries and payroll are covered on the Headcount page; this page covers the rest.

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What approach to use

Statistical is the right default for most OPEX lines. Recurring costs without a clear driver are well-served by a rolling average or a YoY reference. Use driver-based only when a meaningful, reliable driver exists for the cost line. Equipment and rent are good examples: where cost scales with headcount, model it as # FTEs × cost per FTE. For most OPEX items, statistical is simpler and often more accurate. Avoid forcing a driver where the relationship is weak. Use hardcoded for committed costs where the amount and timing are already fixed: a signed contract, an annual software renewal, a booked consulting engagement. A signed contract isn’t a forecast. Enter the number.

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Where to forecast OPEX

  • Directly on the P&L: right for most cases. A rolling average or hardcoded value lives on the cost row itself. Simple to set up, easy to maintain.
  • Supporting sheet: right when a cost area has multiple inputs or needs granular breakdown (software split by vendors, marketing split by channel). The sheet handles the detail; the P&L row references the total.

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Forecasting approaches

Use driver-based when a meaningful, reliable driver exists for the cost line. Add a formula that links the cost to its driver and add the assumption to a separate assumptions sheet.Equipment and rent are good examples where cost scales with headcount:
= "Headcount"[0] * "Cost per FTE"[0]
Marketing spend as a percentage of revenue is another common pattern:
= "Revenue"[0] * "Marketing %"[0]
Avoid forcing a driver where the relationship is weak. A loose correlation produces a less accurate forecast than a rolling average, with more complexity to maintain.