Cost per completed task
Total model and tooling cost divided by the number of tasks completed without human rework. A better measure than cost per call.
Cost per completed task is the total cost of running an AI workflow, including model calls, tools and infrastructure, divided by the number of tasks that were finished without a person having to redo them. It answers the question a buyer actually has: what does one finished piece of work cost?
Cost per call is easy to measure and easy to misread. A cheap call that produces an answer someone must rewrite is not cheap.
In practice
I measure three things for each workflow: the cost per call, the share of tasks that finish without rework, and the human time spent on the rest. Cost per completed task combines them. A change that lowers the cost per call but raises rework usually makes the figure worse, and the evaluation set shows why.
The denominator needs a clear definition of rework. In my work it is any human edit that changes the output's substance, not a typo fix. The definition is written down with the evaluation results so the number can be checked.
Example
[Composite] A drafting workflow moved to a cheaper model and the cost per call fell. Rework rose, and the cost per completed task went up. The team moved only the simple drafts to the cheaper model and kept the complex ones on the stronger model. The completed-task cost was the lowest of the three options.
Common mistakes
- Reporting cost per call as the headline figure.
- Leaving rework out of the calculation because it is hard to measure.
- Comparing completed-task cost between workflows with different definitions of done.
Related terms
Cite this definition
Cost per completed task. Mayur Patil, mayurpatil.ai, updated 2026-11-01. https://mayurpatil.ai/glossary/cost-per-completed-task/