The US postal service says Friday is the deadline if you want your package to arrive by Christmas.
If you use regular parcel post, it needs to be in the mail Friday to get it to it’s destination by the 25th.
If you want to spend a little more, you have until the 20th for first class shipping.
The 21st if you send it priority.
And if you send it express it can be sent as late as the 22nd.