When do price changes take effect on an active subscription

When you update a charge price on a plan, the change applies to the current open (draft) invoice and to all future invoices. Already finalized invoices are immutable and are never altered. This happens because Lago reads prices at the moment fees are calculated, not when events are ingested.

How price changes take effect

Lago calculates usage and applies charge rates at invoice generation time. There is no price snapshot at event ingestion or at invoice creation. The rate is always read from the current charge properties at the moment fees are calculated, whether that is at invoice generation, during a draft invoice refresh, or when the current usage endpoint is queried. Note that this reflects current implementation behavior and may change without notice.

When you update a plan's charges, Lago automatically marks all related draft invoices as ready to be refreshed. Before a draft invoice is finalized, the system runs a full refresh that recalculates all fees using the current charge properties, so the updated price is reflected at finalization without any manual action.

What to do after changing a price

Update the charge price in the plan settings and the new rate is applied automatically when the draft invoice is finalized. If a draft invoice still shows the old rate, it simply has not refreshed yet in the current session. To preview the updated amounts before finalization, trigger a refresh manually with "Refresh invoice" in the UI or via the API.

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