Give finance the assumptions behind the AUD estimate

Separate usage from conversion

Keep provider usage units and billed currency in the underlying record. Present an AUD estimate using an explicitly chosen conversion basis and date, rather than overwriting the original amount.

Distinguish an operational estimate from the final invoice amount. Exchange rates, billing adjustments and contractual pricing can change the result. The finance team needs to know which figures are provisional and how they reconcile later.

Do not hard-code a current exchange rate or public list price into a long-lived estimate without an owner and update process. Use verified current inputs when preparing a real budget.

Transfer the workload assumptions

Document expected task volume, input and output sizes, retry rates, tool usage and manual review. Include a range or scenario where demand is uncertain.

Explain which costs are included and which remain separate, such as storage, evaluation or support effort. A low model-only figure can be misleading if presented as the cost of the entire service.

Keep the assumptions tied to the evaluated configuration. A new model or prompt that produces longer outputs can change the estimate even when user volume stays constant.

Assign reconciliation and control ownership

Name who updates prices, reviews usage differences and investigates expensive tasks. Engineering owns request correlation and resource limits, while finance may own the accounting treatment and budget assumptions.

Document how task-level limits interact with organisation-wide monitoring. Billing alerts and budget actions are useful controls, but they do not replace the application's immediate reservation checks.

Give operators a route to explain unresolved usage after timeouts or provider reporting delays. Do not silently treat missing usage as zero.

Rehearse an estimate-to-actual comparison

Choose a completed period or controlled workload and reconcile task records with available provider usage. Explain differences such as shared costs, delayed reporting or estimates that reserved more than the call consumed.

Use the result to improve assumptions rather than retroactively editing the original estimate without history. A good handover allows finance and engineering to discuss the same workload with clear definitions, and gives both teams a way to update the estimate when the service changes.