Billing anchor cannot be changed after a subscription starts

Once a subscription is active, its billing anchor can't be changed. An anniversary-based subscription that started on the 14th will always bill on the 14th. There's no way to shift it to the 1st or any other date without terminating and recreating the subscription, since changing the anchor mid-flight would require retroactively adjusting open billing periods, which Lago doesn't support.

How it works

Subscriptions are either calendar-based, with billing periods tied to the 1st of the month regardless of start date, or anniversary-based, with periods anchored to the subscription's start date. The anchor determines when billing periods begin and end, and by extension when invoices are generated and charges reset. It's locked at subscription creation.

How to resolve the issue

To bill a customer on a specific calendar date, terminate the existing subscription at the end of the current billing period and create a new one with subscription_at set to the target date. Make sure any billable events for the current period are accounted for before terminating, since this can affect in-progress usage aggregation. If the goal is uniform monthly alignment rather than a specific date, calendar-based billing may be a better fit, since it always aligns periods to the 1st regardless of start date.

This article reflects guidance drawn from customer case resolutions. It is not officially supported documentation and may not apply to all situations.