Hi Laura, I am new and looking into the same thing as you! I think I've found the option when you create a plan you can specify a setup fee: https://developer.paypal.com/docs/api/subscriptions/v1/#plans_create "payment_preferences": { "auto_bill_outstanding": true, "setup_fee": { "value": "10", "currency_code": "USD" }, "setup_fee_failure_action": "CONTINUE", "payment_failure_threshold": 3 }, I don't think you can do it at checkout time without making a plan for each day of the month and then having a different setup fee. Then on your site you'd have to have a table of subscriptions to load the right plan for the day? If anybody else has a better idea? Personally I think I'm just going to have my set plans and then send a separate invoice for the difference. I only have to invoice the extra once a year but I'll let you know if I find a better alternative. Tyler
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