After 21 days on an international trip, and sooner under many airlines’ own rules. What changes when it is.
Airlines call a missing bag “delayed” for as long as they can, because a delay claim is smaller than a loss claim. The rules set a point where that stops.
International trips: the Montreal Convention lets you treat a bag as lost once 21 days have passed from the date it should have arrived. From that day you can claim the full contents up to the cap, not just interim purchases.
Airline rules: several airlines declare a bag lost sooner in their own terms, some after five days, most after 21 to 30. Your airline’s page on this site shows its number.
What changes: your claim switches from “what I had to buy” to “everything that was in the bag”, and the deadline for the written claim is now measured from the day the bag was declared lost rather than from delivery. If the bag later turns up, the airline can ask for items back or offset what it paid.
Work out your own claim → Free. Takes about ten minutes.
No. Send the interim-expense claim now with a line saying you will claim the contents if the bag is not delivered by day 21. The letter this site builds does that.