Lesson 4 of 7
Estimate a bill
7 min read
Ten thousand customer questions a month, answered by AI — is that a few dollars or a few thousand? You can work it out on a napkin.
The whole formula
Cost is just volume × price. Monthly bill = calls × (input tokens × input price + output tokens × output price) ÷ 1,000,000, because prices are quoted per million tokens. Estimate the tokens per call, pick a model's two prices, multiply by how many calls you expect.
Bill = calls × (in×in-price + out×out-price) ÷ 1M. That's the whole thing.
A worked example
Say 10,000 support replies a month, ~800 input and ~200 output tokens each. On a light model that's only a few dollars; on a flagship it can be ten to twenty times that for the same work. The formula makes that gap visible before you commit — which is exactly what the next lesson turns into a lever.
The same task can cost 10–20× more just from the model you pick.
Before building on AI, estimate the bill for 10× your expected volume — that's your worst-case budget, and it takes two minutes.
Estimating in one line
- —Bill = calls × (in×in-price + out×out-price) ÷ 1M.
- —Prices are quoted per million tokens.
- —Estimate at high volume to see the real budget.
What do you need to estimate a monthly AI bill?
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