Year to year, the cheapest time to book holiday flights changes a little bit, but it is always in the spring. According to Hopper, now is the best time to buy your plane tickets to save for Christmas travel. Image from markoknuutila.
You may want to buy ASAP, since Hopper estimates fares will increase steadily as the holiday approaches. Try travelling on Christmas Eve, Christmas Day or New Year's Eve for lower prices. While it may seem early to be booking flights for the holidays, this is one of the most popular travel times of the year, so snagging low fares now can save you quite a bit.