Disclosed is a method for scheduling a refilling of a secondary reservoir of an ambulatory infusion system out of a primary reservoir storing a liquid drug. The method includes repeatedly and automatically carrying out a filling volume assessment routine. The filling volume assessment routine includes: determining, at a present point in time, an estimated filling volume of the secondary reservoir at a future estimation point in time, the future point in time being an estimation time interval after the present point in time, and determining in dependence of the estimated filling volume, if the secondary reservoir shall be refilled at the present point in time.
