# Write the budget in numbers

Lesson 1 of [Evaluate an agent wallet before you fund it](https://agentwalletindex.fyi/academy/evaluate-an-agent-wallet.md), 10 minutes.

Start with numbers, not with a product. A wallet choice makes sense only when you know what the agent will spend.

## Four numbers

1. The most the agent may spend in a month.
2. How many paid calls or purchases it makes in a day.
3. The usual price of one call or purchase.
4. The largest single payment you would accept without asking a person.

If you do not know number 2 or number 3, run the agent for a week on a test balance and count. A guess often leads to a cap that is too tight or too loose.

## Expected monthly spend

Expected spend is calls per day, times 30 days, times the average price, times one plus your buffer. The buffer allows for retries, failed calls and price drift. The planner on this site starts with a buffer of 20 percent.

Example 1. The agent makes 100 calls a day at $0.02 each. The buffer is 20 percent.

- 100 calls times 30 days times $0.02 is $60.
- Add 20 percent and the expected spend is $72.
- With a budget of $93, the headroom is $21. The plan fits.

Example 2. The agent makes 200 calls a day at $0.05 each. The buffer is 20 percent.

- 200 calls times 30 days times $0.05 is $300.
- Add 20 percent and the expected spend is $360.
- With a budget of $100, the headroom is minus $260. The plan does not fit.

When the headroom is negative, change the plan. Cut the number of calls, find cheaper services, or raise the budget on purpose. Do not raise the caps to hide the gap.

## Write the task too

Write what the agent may buy and from whom. "Pay for search API calls up to the budget" can be tested. "Buy whatever helps" cannot.

## Sources

- Agent Wallet Index, Agent spend-limit planner, methodology
- Agent Wallet Index, Agent Spend-Limit Checklist, step 1

Also on the [web page](https://agentwalletindex.fyi/academy/evaluate-an-agent-wallet/write-the-budget-in-numbers).