Choosing the right Stripe subscription model if pricing depends on another numerical attribute

Question

I have little experience with payment gateways, and am trying to figure out how to synthesize the type of subscription billing that I am looking for: the monthly price gets rebalanced once a year, based on another attribute (a number that can get as high as seven or eight digits).

So, for example, the monthly subscription price as of January 1st will be a % of a user's credit card debt balance as of Dec 15th in the prior year. But the debt balance can get very high / does not have a cap.

I looked at the Stripe documentation to figure out of there's a way to do this. The only thing I could come up with is to use unit_amount in metered pricing and tying this to the credit balance. In other words, I would grab the debt balance number and use it as the unit_amount, and then apply a %. But then I need to also forward bill, so I trick the logic into shifting by a month, which seem impractical.

Alternatively, I am not sure I could do this with per seat pricing (e.g. $1 in debt = 1 seat). But I assume there's a max to the number of seats (i.e. someone cannot have, say 1m seats). I just couldn't determine this from the documentation...

That's what I was thinking, anyway. Perhaps there's a better way?

Answer 1

You've got a couple different options here:

1. At the start of the year you update the Subscription to a new price based on the calculations of the customer's credit card debt balance by specifying items[0].price_data. Setting items[0].price_data (see the api ref) allows you to create an "in-line price" that as part of the updating the Subscription, so you don't have to create one separately through a separate API request. If you haven't seen Stripe's docs on how to update the price of a Subscription you can see an example here, and you'll likely want to read about proration_behavior as well.
2. You have a single Price where 1 seat = $1 in debt, and you control how much you want to charge by changing the number of seats for the Subscription. I don't think Stripe has a limitation to the number of seats (as long as it's a valid integer), but they do have a limitation on the maximum amount you can charge which you can read about here. For USD the maximum charge amount is $999,999.99, so the maximum quantity would be you could specify for a $1 price is 999,999.
3. You could look into using metered pricing, but given that you don't want to bill at the end of the billing cycle the other two options seem better.

I think the first option (updating the price year by year) is your best one, but definitely try all of them out in test mode and take a look at how the Invoices look to see which one you like best.