Generally within 2 weeks after moving out. Depending on local rules, deregistration may in some cases already be possible during the week before moving out.

Under section 21(4) of the Federal Registration Act, giving up a secondary residence can be reported either to the registration authority for the secondary residence or to the authority for the sole or main residence.

Have your identity document, details of the secondary residence and the move-out date ready; the local registration authority may request additional information.

Do not confuse this with deregistration during a normal move within Germany: if you take a new main residence in Germany, you generally register the new home and the former main residence is handled through that process.