If you still haven't mailed out your holiday cards, you might want to hurry since Tuesday is the last day the Post Office can guarantee delivery by Christmas of First-Class Mail.

This week is the busiest week for mailing, shipping and delivery with presents, letters and Christmas cards being sent all over the country.

The U.S. Postal Service is expected to deliver about 15 billion pieces of mail and 850 million packages this holiday season. 

If you need to send something but couldn't make it to the Post Office on Tuesday, you can still get your cards to their destination by Christmas if you send it through Priority Mail tomorrow.