Will long-term storage cost double if inventory is kept in FC for more than year

Long-term storage will start to cost you after your inventory stays in an Amazon warehouse for the year (365 days) or so, there are no doubles or anything like that.

The long-term storage charges are applicable only if your inventory is in Amazon warehouse for more than one year, so there is no chance of doubling after one year

Long-term storage costs will change with time.

No, the long-term storage fees will not double even if your product is kept in an Amazon warehouse for more than a year.

If your inventory in an amazon warehouse for longer than one year then amazon will charge the long-term storage according to policies like if your inventory will complete the 1 year on this 30 December and amazon announces the new long-term storage costs from now to onward then amazon will charge you the new increased costs for your long term excess inventory if it stays in FC longer than 1 year.

No, even if your product stays more than a year at an Amazon warehouse, the long-term storage fees won’t double.