The USPS has posted the deadline dates for those planning to ship in time for holidays. many people can't make it to be with everyone for the holiday season so they end up shipping their gifts. The post office wants to make sure they can get your gift to its destination in time for Christmas morning so they have posted the deadlines well in advance of the rush.

Domestic USPS Mail-By Dates to assure delivery by December 24th

 First-Class Mail  Dec 19
 Priority Mail  Dec 20
 Priority Mail Express  Dec 22