Christmas & New Year's: The Christmas and New Year's holiday travel window is more or less a 17-day period that overlaps the two holidays by about five or six days, according to statistics gathered from the U.S. Bureau of Transportation Statistics. Peak days always depend on when the weekends fall in relation to the holidays, since lots of people want to travel over convenient long weekends. Note that it's not unusual to see flights departing on Christmas Day, New Year's Day and sometimes the days immediately following or preceding the holidays that are cheaper than departures a few days out, depending on how they fall during the week. If you're booking a holiday trip, use your booking engine's flexible dates option to see which days will save you the most money.
Spring Break: Spring break peak travel dates vary by destination, but generally extend from late February through the beginning of April. Most colleges and universities have spring break in March or even late February, while families with school-age children vacation around Easter, which is usually in late March or early April. Watch out for higher fares to beach and family destinations like Florida and the Caribbean during this time.
If you're visiting a destination that attracts the college set, such as Cancun, Punta Cana or Nassau, but you're hell-bent on avoiding "bikini contests, wet T-shirt contests, male hard body contests, porn stars, movie stars, rock stars and rap stars," as spring break in Panama City Beach, Florida is described on TripSmarter.com, here's a tip. Take a look at this chart on the Trip Smarter site, which outlines the spring break dates for American colleges and universities each year. Avoid planning your beach vacation around those dates -- unless, that is, you're down for a wild time.
Summer: Summer is high season for myriad destinations and fares are accordingly driven higher by demand. The crest of summer travel is from Memorial Day to Labor Day, during which fares to most U.S., Canadian and European destinations are at their peak. Three-day weekends around summer holidays like Memorial Day or the Fourth of July are particularly expensive times to fly. If you can put off your trip till mid- September or go in May instead of June, you'll likely pay less than you would over the summer (not only for airfares but also for hotels once you arrive).
Thanksgiving: Peak Thanksgiving travel dates are pretty cut and dried year after year, as the holiday always falls on the fourth Thursday of November. The period from Wednesday through Sunday around Thanksgiving wins the award for Busiest Travel Time of the Year. So when's the best time to depart for the big family feast? The busiest and most expensive days are the Wednesday before and the Sunday after Thanksgiving. Flying on Thanksgiving Day itself typically offers the cheapest possible fares; the day after is often a pretty good deal as well. As with Christmas and New Year's, you'll save by zigging when others zag; while everyone else plans to be back at work the Monday after Thanksgiving, you could save by extending your long weekend and flying home that day instead of Sunday.