Billing periods are a core object in generating invoices.
Billing period definitions set the dates on which a customer invoices, contain the group of subscriptions to invoice together, and several invoicing overrides. Billing periods define when invoices will be generated, the service dates of charges on those invoices, and what dates to prorate charges to.
Billing periods are created and reused as a subscription is created for a customer. It will reference the customer's billing options for when and how to bill, the account's options, and then any pre-existing billing periods on that customer, depending on those options.
They are defined based on the options for when and how to bill. These options can be set at the account level or overridden on a per-customer basis. Some of these options will also check for pre-existing billing periods on a customer.
Billing period preferences, such as the billing date, can be set on the Settings>Financial>Default Billing Period Preferences page. Changing these options does not affect existing draft subscriptions, active subscriptions, or billing periods. Only completely new subscriptions will be affected. This includes not affecting existing draft subscriptions.
Subscriptions on the same billing period will be billed on the same invoice. These billing periods define the service dates on invoices for subscription product-related charges.
See Configuring Billing for more information.