Be a little flexible with your flight itinerary and you could save some cash; that's because some days are cheaper for flying than others. There are three days specifically that are cheapest for air passengers. Those days are likely to yield the best rates for departures and arrivals, but remember: This isn't an exact science.
The universal consensus seems to be that airfares tend to be lowest for flights that depart on Tuesdays and Wednesdays. That's what George Hobica of our sister site AirfareWatchdog says, along with CheapAir. Some sources, including Fodor's, add Thursday, and others, including our own Josh Roberts and FareCompare, add Saturday.
Expedia's 2015 Travel Trends White Paper posts the most comprehensive analysis of the "when to fly" question. Expedia concludes that, for long-haul flights, leaving on Thursday and returning on Monday costs around 20 percent less than leaving on Friday and returning on Saturday. The lowest in-and-out combinations tend to cluster in the range of outbound Sunday, Tuesday, Wednesday, and Thursday; returning Sunday, Monday, Thursday, and Wednesday. For short-haul trips, Expedia's lowest-fare groupings are Monday, Tuesday, and Wednesday both ways.
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Does time of day matter? Oddly enough, you find very little data on this question. Overall, afternoons are the "rush hour" for flying, so you find fewer good airfares on afternoon flights. On some short-haul routes, early mornings are also rush hour, as business travelers start their one-day in-and-out quick trips. Still, others say the dinner hour is a good time to fly.
On domestic routes, fares for overnight red-eye flights are often lower than for daytime flights--but you have to put up with the miseries of sitting up all night in a tiny economy seat.
―By Ed Perkins