The US Postal Service expects to deliver more than 15 billion pieces of mail this Holiday season, with the week of December 18th – 24th most likely the busiest mailing days of the year.

Three billion pieces of first class mail will be processed and delivered during that week alone. In the two weeks leading up to Christmas, 200 million packages will be delivered per week.

Here’s a list of domestic shipping deadlines to ensure gifts arrive by Christmas:

December 16th: First Class Packages

December 19th: First Class Mail (Includes greeting cards)

December 20th: Priority Mail

December 22nd: Priority Mail Express