When Calendar Billing is enabled with 'Immediate' alignment, the subscriptions will follow the billing date that is set and prorated charges will be collected. 

We have migrated to new Self-Serve Calendar Billing configuration from 23 March 2023. Self-Serve Calendar Billing allows you to add multiple Site-level & Plan-level configurations also supports Yearly billing frequency. With this new configuration, you can manage both SaaS and E-Commerce business. Besides, the Advance trigger allows you to set calendar billing for specific events. Reach out to our support to enable this feature on your site.

Example: When the common billing date is set as 15th and a customer signs up for a $100 plan on the 2nd of a month, a prorated charge of ~$47 will be collected from the customer for the term 2nd to 15th.

However, if a past start_date is specified while creating the subscription, Calendar Billing will be applied with 'Delayed' alignment and not 'Immediate' alignment. 

Example: When the common billing date is set as 15th and a subscription is created ($100 plan) on Jan 2nd with the start_date specified as Jan 1st, the following will be the charges:

$100 collected on January 2nd for the period January 1st (according to the start_date) to February 1st

~$50 collected on February 1st for the period February 1st to February 15th