Setting subscription quantities
By default, each subscription is for one product, but Stripe allows you to subscribe a customer to multiple quantities of an item. For example, say you run a hosting company and your customers host sites through it at a cost of 9.99 USD per site, per month. Most customers host a single site, while some host many. You could create prices for one site (9.99 USD), two sites (19.98 USD), and so forth, but a better approach is to subscribe customers to a quantity with a 9.99 USD unit price.
Subscriptions have two kinds of usage-based billing: metered billing, and per-seat licensing. You can enable these billing models by setting the value of the recurring[usage_type] attribute when creating a price. You can only specify a quantity when creating a subscription with a recurring[usage_type] of licensed. If you want to have granular billing for usage that fluctuates within a billing interval, consider using metered billing instead of quantities.
Setting multiple quantities
To set the quantity on a subscription, provide a quantity value when creating or updating the subscription:
You still bill multiple quantities using one invoice, and you prorate them when the subscription changes. This includes when you change subscription quantities.
Charging different amounts based on quantity
In some cases, you might want to adjust the cost per seat based on the number of seats in a subscription. For example, you could offer volume licensing discounts for subscriptions that exceed certain quantity thresholds. You can use tiers to adjust per-seat pricing.
Quantity transformation
When you bill your customers, you might want to track usage at a different granularity than you bill. For example, consider a productivity software suite that charges 10 USD for every 5 users (or portion thereof) using the product. Without quantity transformation, they would need to increase the quantity of the subscription item by 1 for every 5 users.
| Number of Users | Subscription Item Quantity Reported to Stripe | Total |
|---|---|---|
| 1 | 1 | 10 USD |
| 3 | 1 | 10 USD |
| 5 | 1 | 10 USD |
| 6 | 2 | 20 USD |
| 7 | 2 | 20 USD |
With the transform_quantity parameter, you can instruct Stripe to transform the quantity before applying the per unit cost. The following subscription allows you to naturally report the current number of users as the subscription item quantity—Stripe’s billing system divides the quantity by 5 and rounds up before calculating by the unit cost.
Currently, the only available transformation is division, using the divide_by parameter in conjunction with the round parameter.
You can only use transform_quantity with billing_scheme=per_unit—it’s incompatible with tiered pricing.
Rounding
The previous example showed a subscription that charges for every 5 users rounding up, that is, 6 divided by 5 results in a quantity of 2. For use cases where you don’t want to charge for a portion of usage, like charging for every full gigabyte of usage of a broadband internet service, you can also pass down as the value of round.
Metered usage
You can also apply transform_quantity in conjunction with metered billing. This transformation applies to prices with recurring[usage_type]=metered at the end of a billing period in the same way it applies to quantity for prices with recurring[usage_type]=licensed.
A marketing email service that creates a metered price to charge 0.10 USD for every full 1000 emails sent might look something like this:
With this subscription, usage can be reported per email and you can bill the customer 0.10 USD for every 1000 emails they send.