How to Budget AI API Costs Before You Launch

1. Define a successful task

Write down what counts as success before estimating spend. For a document summary, that might mean a valid response that includes the required sections and stays within your length limit. Count unsuccessful attempts separately. Your cost per successful task should include the attempts you paid for along the way.

Create separate estimates for different workflows. A short classification request and a long document analysis should not share one average until you know their actual traffic mix.

2. Measure representative requests

Choose a small collection of realistic, sanitized inputs. Include short, typical, and unusually long examples. Record the input and output usage reported for each attempt, the outcome, and any extra requests your application makes.

Use those observations to build a baseline and a busy-day scenario. If you have no running integration yet, label your token counts as assumptions and replace them after testing. Do not assume that a shorter visible answer proves lower billed usage; confirm the supplier's billing definition.

3. Calculate the request budget

For a simple service that charges only for input and output tokens:

Request cost = input tokens ÷ 1,000,000 × input rate + output tokens ÷ 1,000,000 × output rate

Hypothetical example, not a supplier quote: assume 10,000 monthly tasks, one request per task, 1,500 input tokens and 400 output tokens per request. Assume rates of $1 per million input tokens and $4 per million output tokens. Each request costs $0.0031, producing a $31 monthly estimate.

If paid retries add 10% more requests with the same assumed usage, the estimate becomes $34.10. A further 20% planning reserve brings the working budget to $40.92. These percentages are illustrative allowances, not observed failure rates or forecasts. Different retry sizes would require a different calculation.

4. Check what the formula leaves out

Ask whether cached input, additional billable token categories, tools, storage, minimum commitments, taxes, or currency conversion apply. Include only charges relevant to your chosen service, using its written terms. Keep your own hosting and support expenses in a separate line so you can see the full application cost.

5. Turn the estimate into a limit

Decide what your application should do near its budget: alert an operator, pause optional jobs, or ask users to shorten large inputs. Verify that any supplier spending control behaves as expected before relying on it. Review actual spend against successful tasks after launch and update the assumptions.