Record the plan and billing route
OpenAI describes shared Work and Codex usage within a ChatGPT plan. An API key follows API access and billing; it is not equivalent to every cloud feature of ChatGPT-based access. Record sign-in, available functionality and a dated current pricing source. A model name alone is not a cost figure.
Use the accepted change as the cost unit
Record consumption plus preparation, correction, testing and review time for several comparable tasks. Do not compare a difficult defect with a simple text change. The denominator should be an accepted task or another clearly defined deliverable. This reveals whether low model consumption merely creates more human rework.
Account for peaks and operating effort
Separate recurring cost from one-off setup. Add parallel tasks, retries and maintenance as explicit assumptions. Show a baseline and a higher-usage scenario. Verify actual limits and consumption controls in the account used. An example calculation is a planning aid, not a guaranteed monthly invoice.
Decision matrix
| Decision point | Proceed when | Stop when |
|---|---|---|
| Cost assumptions | Documented: current plan, usage pattern, review time and avoided work. | Scope, data or accountability remains unresolved. |
| Measurement baseline | A cost calculation separates verified plan assumptions, observed usage and measured review time. The comparison uses the same delivered engineering task and makes uncertainty visible. | There is only an unevaluated demo without acceptance evidence. |
| Budget decision | Owner, approval, fallback and next review date are defined. | Avoid: stale price values without a review date. Undated prices or unmeasured usage assumptions must not be presented as reliable budget commitments or guaranteed savings. |
Keep it verifiable
Primary sources
- OpenAI: PricingSource checked:
- FinOps Foundation: Unit economicsSource checked:
