Cheapest day to book flights: what studies and airlines say

There is no day that is reliably cheapest. A 2019 Which? analysis of Skyscanner fares found Sunday the cheapest day to book, but a 2025 Which? analysis found the best time to book depends on the destination and the month, from five weeks to six months ahead. What does not change is the total you pay, so check it, with bags, before you buy.

This guide sets out what those two studies say, why a single rule does not hold, and the checks the Civil Aviation Authority (CAA) and airlines point to before you pay: the full price, baggage, the name on the ticket and your passport. We do not sell tickets and we quote no fares.

Both studies come from Which? and both use Skyscanner fares, but they were published almost six years apart and they frame timing differently. The table sets them side by side.

The 2019 finding about Sunday rests on 2017 and 2018 fares, so treat it as a dated result, not a rule for today.

In 2019 Which? said flight prices change based on demand, so it is impossible to give a definitive answer on how far ahead to book to always get the cheapest fare. Its 2025 figures show why: the same month gives very different windows for different places.

The CAA adds a second reason a rule falls short. Its planning your trip page says flights and holidays can cost more at busy times, including school holidays, and that it may be cheaper if you can be flexible with your dates, or fly early in the morning or late at night.

The CAA says airlines must show you the full price upfront, including mandatory charges and taxes such as Air Passenger Duty. It also says there may be optional charges for some bags or seat selection.

Bags are one place a low fare can change. The CAA's baggage allowance page says your air fare may not include hold luggage, and that the luggage cost will not be shown in the price you see at first. It adds that the price that initially seems the cheapest might not be, once the add-ons are counted.

The Competition and Markets Authority (CMA) guidance on unfair commercial practices says that showing an initial headline price and then adding mandatory charges as you go through a purchase, sometimes called drip pricing, is prohibited.

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  The name: The CAA calls it essential to spell passengers' details correctly when you book, as many airlines charge for changes. easyJet asks that the full name matches the ID you will travel with, including middle names.
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  Your passport: For France, GOV.UK says the passport must have a date of issue less than 10 years before the day you arrive and an expiry date at least 3 months after the day you plan to leave the Schengen area. Check your own destination before you buy.
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  Baggage: Check whether hold luggage is included, and what the allowance is. The CAA says allowances vary across airlines and destinations.
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  Opt-ins: The CAA says to check that the airline does not automatically opt you in to paying for a hold luggage allowance you do not want.
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  The terms: The CAA recommends reading the airline's terms and conditions when you book. They say what you must do as a passenger and what you can expect from the airline.

Your entry rules are on the GOV.UK page for each country: France entry requirements is one example, and our guide to entry requirements for British passport holders covers the rest.

Each airline sets its own terms, so read the one you book with. As an example, easyJet's change flight and change name page says title changes and spelling mistakes of up to three characters per name can be corrected online free of charge, and that more than three characters means contacting customer services.

The same page says a change fee applies per passenger changed, per flight, and that a flight change also carries the fare difference if the new fare is higher. If the new fare is lower, it says no refund is made.

A ticket is one item on a longer list. Our holiday packing list starts with documents, and our travel tips for UK travellers collect the other checks in one place.

• Is Sunday the cheapest day to book flights?

  Which? said so in 2019, based on Skyscanner fares from 2017 and 2018, and named Wednesday as the most expensive day. That is a dated finding, not a current rule.

• How far ahead should I book a flight?

  Which? found in 2019 that around three months ahead was cheapest, with six months for peak summer. In 2025 it found windows from five weeks to six months, for example 5 weeks for Faro and 26 weeks for Paris in August. Which? says no definitive answer exists.

• Is it cheaper to fly early in the morning or late at night?

  The CAA says it may be cheaper if you can be flexible with your dates, or fly early in the morning or late at night. That is about the time you fly, not the day you book.

• Does the price shown include everything?

  The CAA says airlines must show the full price upfront, including mandatory charges and taxes such as Air Passenger Duty. It lists optional charges for some bags or seat selection separately.

• Is hold luggage included in the fare?

  Not always. The CAA says your air fare may not include hold luggage, and that the cost will not be shown in the price you see at first. Check the allowance, which varies across airlines and destinations.

• Does the name on the ticket have to match my passport?

  The CAA calls it essential to spell passengers’ details correctly when you book. easyJet asks that the full name matches the ID the passenger will travel with, including middle names.

• What if I spell a name wrong when booking?

  On easyJet, spelling mistakes of up to three characters per name can be corrected online free of charge, and more than three means contacting customer services. The CAA warns that many airlines charge for changes, so check your airline’s terms.

• How long must my passport be valid for a trip to France?

  GOV.UK says the date of issue must be less than 10 years before the day you arrive, and the expiry date at least 3 months after the day you plan to leave the Schengen area. Other countries set their own rules.

• Is drip pricing allowed on flight bookings?

  CMA guidance says showing an initial headline price and then adding mandatory charges during a purchase is prohibited. The CAA lists optional charges for some bags or seat selection separately, so read the total before you pay.