RADIUS can also be used for accounting. This involves a RADIUS message at start and end of each connection, and also interim accounting updates.

Interim accounting is done on a snapshot basis. Normally this is hourly. On the hour, within a second, the details are recorded and then sent by RADIUS. The RADIUS updates may take many minutes to be sent and confirmed by a RADIUS server, but the timestamp on the messages is the hourly snapshot. This is useful where an ISP is charging differently at different times of day.

Interim updates can also be sent based on reaching a pre-set time or data usage level defined in the authentication RADIUS response.