According to AARP:
The cheapest day to fly is on the holiday itself: Thanksgiving Day, Christmas Day and New Year's Eve.
In general, Friday and Sunday are the priciest days to fly. During the holidays, the worst days are the Wednesday before Thanksgiving and the Sunday after it, as well as Dec. 21-24, Dec. 26-30 and Jan. 2-5. You'll pay between $20 and $150 extra for flights on these dates.
Get all of the tips including on how to bundle to save even more,