Christmas is on a Thursday, most international destinations could received delivery by Christmas even if they order as late as December 21st and choose UPS Express (or Express Saver) shipping. Order by December 17th and choose UPS Expedited shipping. For cheaper regular mail shipping anytime after this Friday and you’re really pushing your luck, though it is possible you can still get it ordering as late as perhaps the 12th, it would not be guaranteed. For domestic US shipments you can order next day air by the morning of the 23rd and have it delivered in time for Christmas. 2nd day air on the 22nd, 3 day select on Friday the 19th. Ordering by the 17th should allow regular ground shipping to reach you anywhere in the US (except Alaska and Hawaii), the closer you are to Michigan the longer you can wait on that ground cutoff.
