What free-tier and trial users cost you in API spend — and per paying customer.
Trials burn tokens whether or not they convert, so track cost per acquired customer, not just total spend. Size the paid-side margin on the AI SaaS margin calculator and per-user cost on the cost per active user calculator.
The AI Free Trial Burn Calculator estimates the monthly API cost of the free users on your AI product before any of them convert to paying. It multiplies your free-trial signups per month by the tokens each trial user consumes and the price per million tokens to produce your total monthly free-tier spend, then divides that spend across the users who actually convert (signups times the trial-to-paid rate) to show the cost per paying customer. The main drivers are signup volume, tokens burned per trial, the model's price per million tokens, and the conversion rate.
The key trade-off is generosity versus burn: raising token allowances or signup volume helps acquisition but inflates free-tier spend, and a low conversion rate concentrates all of that cost onto each customer who pays. Watch cost per paying customer against your gross margin. If free-trial burn per convert approaches a customer's contribution, tighten token caps, gate expensive models behind paid tiers, or improve conversion before scaling signups.
Multiply trial signups by the tokens each consumes by your per-token price. Then divide the total by how many convert to paying to get your true API cost per acquired customer — the number that tells you whether the free tier pays for itself.
Cap tokens or requests per trial user, require a card or email verification, rate-limit aggressively, and use a cheaper model for free tier than for paid. Freemium AI products routinely find that a small fraction of free users drive most of the burn.
Cost at different volumes:
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