How we know: Sources are listed at the end. The percentages are quoted from Google Flights' and ARC/Expedia's published analyses of their own data, not from Wildly's price checks.
Two different questions hide inside "cheapest day to fly": the day you depart and the day you buy. The published data is clear that departure day matters and purchase day barely does.
Departure day: midweek is cheaper
Google Flights' analysis of its price history found that flying on Monday, Tuesday or Wednesday has been about 13% cheaper than flying Friday, Saturday or Sunday, and about 20% cheaper for domestic-only trips (Thrifty Traveler on Google Flights data). ARC and Expedia's ticketing data points the same way for international travel: departing on a Thursday saved up to 15% compared with Sunday, the priciest day to leave (ARC / Expedia 2025 Air Hacks).
The mechanism is simple. Leisure travellers want to leave Friday or Saturday and return Sunday; business travellers cluster on Monday out and Thursday or Friday back. Tuesday and Wednesday departures have the least demand, so airlines price them to fill seats.
Return day counts too
A round trip has two legs, and the weekend premium applies to both. Returning on a Sunday after a week abroad is the most contested slot; shifting the return to Monday or Tuesday often lowers the total even when the outbound is unchanged. When you compare fares, check both halves of the trip.
Purchase day: ignore the Tuesday myth
In Google Flights' data, the cheapest day of the week to book was only about 1.3% cheaper than the most expensive day (Sunday). ARC's data, which measures what people actually paid, found Sunday the cheapest day to buy by up to 8% compared with Friday. The two datasets do not even agree on which day wins, which tells you the effect is small and unstable. Spend your flexibility on departure day, not on which weekday you click.
How to find the cheapest departure day for your route
- Use a flexible-date or calendar view on Google Flights or the airline's site and look at a whole week, not a single date.
- Compare Tuesday/Wednesday out with Tuesday/Wednesday back against your original plan.
- If one leg must be on a weekend, keep the other midweek.
- Check what the route is pricing today on its page, for example JFK to Paris, LAX to London or Chicago to Tokyo, then set a price alert with a flexible-date window so a cheaper adjacent day can trigger it.
Exceptions
- Long weekends and holidays. Around Thanksgiving, Christmas and national holidays, the "cheap" days move; the days immediately before and after the holiday carry the premium.
- Beach and resort routes. Saturday-to-Saturday package patterns can make Saturday the busiest day on routes to Cancún or the Caribbean.
- Routes with few weekly flights. If a route only operates three days a week, the cheapest day is whichever of those three has spare seats; a calendar view will show it.
FAQ
What is the cheapest day to fly internationally? In the published data, midweek (Tuesday and Wednesday, with Thursday also strong for international departures) is consistently cheapest; Friday and Sunday are the most expensive.
Is it cheaper to book flights on Tuesday? No meaningful difference. Google Flights' data puts the booking-day gap at around 1.3%.
Does the time of day I fly matter? Early-morning and late-night departures are often cheaper because fewer people want them, but the effect varies by route; check the day view.