AI service free trials by days or usage: a cost cap and 3 endings
Choose what happens when an AI service's free trial ends first, and bound it by usage if you need a cost cap.
Key points
- Choose the ending before days or usage
- Need an AI cost cap? Bound by usage
- No card? Give a credit balance instead
- No countable unit? Bound by days
Contents
Choose the ending first: cancel, pause or invoice when the trial ends
A&A perspective
Before deciding whether to bound a free trial by days or by usage, choose what happens on the day it ends: cancel, pause or invoice. A free trial here means the range a new customer can try without paying, bounded by days or by usage.
From the sources
Stripe, a payment service, documents that a business can configure what happens when a trial ends with no payment method, such as a card, on file. The three options are to create an invoice, to cancel, or to pause until the subscription is resumed.
From the sources
If you choose nothing, the default applies, which is to create an invoice. If that invoice is not paid, the documentation says the subscription moves to a past-due state.
A&A perspective
Automate & Augment (A&A), which writes this article, reads this as a decision that is already made even if you make none. The answer it has made is that people who only tried the service and never added a card still get an invoice.
From the sources
The same documentation asks a business that receives a cancel or pause notice to stop giving that customer access. During a pause, it allows access to stay off until a card is added and the subscription resumes.
A&A perspective
The payment service stops the billing; your own team stops the service. If that step is missing, people whose free trial has ended keep using it, and only the AI cost keeps going out.
A&A perspective
The choice is easier if you ask whether the person has finished trying. Pause suits someone who has not finished. Cancel suits someone who tried and said no, and an invoice suits only someone who wants to keep going.
A&A perspective
When you take this to your manager, it fits on one line, such as "Customers with no card are paused on the day the trial ends." You can write it before the boundary is decided, so decide it first.
A&A perspective
If you use a payment service other than Stripe, check first whether you can choose what happens when a trial ends, and what happens if you choose nothing.
Need a cap on AI cost? Bound by usage
A&A perspective
If you want to show your manager one number for the worst case of what free use can cost, bound the free trial by usage, not by days. A boundary in days puts no ceiling on the cost of running the AI.
From the sources
Anthropic, the company that makes the generative AI Claude, lists the price of calling its AI from your own service by the amount of text the AI reads and writes. The unit is a price per million tokens; a token is the small unit an AI uses to count text.
A&A perspective
AI cost grows with the amount processed, not with the number of days. With a 14-day free trial, someone who barely touched the service and someone who used it heavily every day reach the end on the same date. The first costs almost nothing; the second has no ceiling.
Hypothetical example
For example, suppose you launch a new service that summarizes meeting records. Here we assume, only for the calculation, that the AI cost per summary is 30 yen. This is not a result from any A&A client.
Hypothetical example
Someone who uses 10 summaries a day during a 14-day trial uses 140 in total, which costs 4,200 yen. Because each user decides how much to use, you cannot work out the total cost of the free trial in advance, even for 100 users.
Hypothetical example
With "30 summaries to use within 30 days", the cost per person stops at 900 yen. With 100 people trying, the ceiling is 90,000 yen, and that is a number you can give your manager.
A&A perspective
To get your own number, multiply three things: the AI cost per unit, the number of units you give away, and the number of people trying. Whoever builds the service can tell you the AI cost per unit.
A&A perspective
A usage boundary also lets you test the assumption that 30 summaries are enough to see the value, using the counts people actually used. If it is too few, raise it; if units are left over, lower it, and you decide by the counts.
A&A perspective
The table below sets out, for your manager, the precondition for each way of drawing the boundary and what happens when that precondition fails. The cost ceilings come from the assumed calculation in this section (30 yen per summary).
| Boundary and cost ceiling (assumed) | Precondition | What happens when it fails |
|---|---|---|
| By days (14 days). No cost ceiling | The value can be seen within the period | People who barely used it reach the same deadline; heavy users' cost has no stop |
| By usage (30 summaries). Ceiling of 900 yen per person | Customers can say in their own words how much is left | The remainder cannot be read and questions increase; with no card it does not fit the trial feature |
| Both (30 summaries within 30 days). Ceiling of 900 yen per person | You tell people in advance which is expected to run out first | You cannot explain why it ended, and the ending looks unkind |
| Neither the boundary nor the ending decided. No cost ceiling | None | People with no card get an invoice by default, and unpaid ones go past due |
Without a card, give a credit balance
A&A perspective
If you want to bound by usage without asking for a card, consider giving the free part as a prepaid credit balance rather than as a trial period. In Stripe's trial feature, a trial with no card cannot include items billed by usage.
From the sources
Stripe's trial documentation states the limitation that a free trial with no payment method cannot include items billed by usage. For trials where the customer adds a card or another payment method, the same documentation describes how to attach a usage-based price.
A&A perspective
That leaves two paths. One is to ask for a card first and run a trial bounded by usage. The other is to ask for no card and give the free part as a credit balance.
From the sources
Stripe's billing credits documentation calls a balance given to a customer in advance or as a promotion a credit, and tracks it customer by customer. A balance stops being usable once it is used up or expires. It adds that businesses often give promotional credits in limited amounts, usually with an expiry date.
From the sources
On expiry, it says credits do not expire unless the expiry field is set. It also says a balance can only be applied to the charge for items billed by usage.
A&A perspective
With a balance, the free part ends when it is used up, not on a set date. The signal that it is over comes from how the customer uses it, not from the calendar.
A&A perspective
On the other hand, without an expiry date some people will come back six months later and use what is left. Set both an amount and a period, as in "30 summaries to use within 30 days", and both the cost ceiling and the closing date are fixed.
A&A perspective
The documentation does not say whether you can give a balance to someone with no card on file. Before you build it, check with the payment service's documentation or with whoever builds the service.
If users can't say what is left, bound by days
A&A perspective
If customers cannot say in their own words how much they have left, as in "I can use five more", bound by days rather than by usage. A free trial whose remainder cannot be read feels, from the customer's side, like one that could end at any time. With days, the end date is known in advance.
A&A perspective
A unit people can count is one where each piece is about the same size, such as one summary or one draft. With a unit whose length varies, such as one conversation with an AI, the cost of a single use can differ widely and nobody can say what is left.
A&A perspective
Even with a countable unit, bounding by usage means your own team decides how to show what is left and how to warn people before the end.
From the sources
According to Stripe's billing credits documentation, a balance is only taken off a bill when the invoice amount is finalized. Until then, the available balance on screen can show zero while the ledger still holds a balance, the documentation says.
A&A perspective
In other words, the remainder on screen and the real remainder can differ for a while. If you bound by usage, you also decide which remainder to show on the customer's screen.
From the sources
The documentation also sets defaults for warnings before the end. In Stripe's trial documentation, the notice sent to the business before a trial ends goes out three days before the end by default. The business can use it to send its own reminder email. Stripe's own reminder emails are sent seven days before the end.
A&A perspective
With a boundary in days, the timing of warnings has a default like this. With a usage boundary there is none, so you also decide at what share of the remainder to warn people, and how many times.
A&A perspective
Whichever boundary you pick, write what happens on the last day to people with no card as a separate line from the boundary itself. When the boundary and the ending share one line, the ending tends to drop out.
A&A perspective
The sources are all payment and pricing documentation and do not say whether to choose days or usage. The way of choosing is A&A's interpretation. Defaults in the documentation can change, so this article is based on the versions read on October 23, 2026.
Summary
A&A perspective
Choose cancel, pause or invoice for the day the trial ends first. If you choose nothing, an invoice goes out.
A&A perspective
If you want a cap on AI cost, bound the free trial by usage.
A&A perspective
If you bound by usage without a card, give a credit balance instead of a trial.
A&A perspective
If customers cannot say what is left, bound by days.
Whether to bound a free trial by days or by usage is a choice to make after you decide how it ends. Write one line for what happens on the last day to people with no card, bound by usage if customers can count what is left and by days if they cannot, and take that to your manager with the cost ceiling.
FAQ
Should a free trial skip asking for a card?
It depends on whether you want to bound it by usage. In Stripe's documentation, a trial with no card cannot include items billed by usage. To bound by usage, either ask for a card first or give the free part as a credit balance.
If customers have free credit left over, can it be refunded or cashed out?
Stripe's documentation prohibits giving credits as gift cards or as stored value that can be used beyond your own products and services. A&A's view is that leftover free credit should not be described as if it were value that can be refunded.
How many free units or days are right?
This article does not give a right number of units or days. The 30 summaries are a number assumed for the calculation, not a recommendation. Set a working guess for how many units it takes to see the value, then watch how people use it and decide whether to raise or lower it.
Sources & editorial note
Primary pages read for this article. Publication dates below belong to the sources; access dates record our research.
- Configure trial offers on subscriptions
Stripe · undated documentation page
Accessed 2026-10-23 - Billing credits
Stripe · undated documentation page
Accessed 2026-10-23 - Pricing
Anthropic · undated pricing page
Accessed 2026-10-23