How to book a cheap flight

Flight pricing looks random and is not. Airlines divide every aircraft into fare buckets, each with a set number of seats, and the price you see is simply the cheapest bucket still open on the day you look. Understanding that one mechanism explains almost everything else: why prices jump overnight, why the same seat costs three different amounts, and why refreshing the page does not help.

Here is what actually moves the number, in rough order of how much money it saves.

1. Be flexible with dates - it is worth more than every other trick combined

Nothing else comes close. Moving a departure by two or three days routinely changes the fare by 30–50%, because you slide into a bucket that has not sold yet.

Use the month view or flexible-date grid that every major search engine offers, rather than searching one specific date. Look at a whole month at once and the pattern becomes obvious: a handful of cheap days, a wall of expensive ones around school holidays, and a slow climb towards the weekend.

If you can move your dates and you refuse to look at the calendar view, you are leaving the largest single saving on the table.

2. Book in the right window

Fares are usually cheapest somewhere in the middle of the booking curve, not at either end. Too early and only the airline's standard fare is loaded; too late and the cheap buckets are gone.

• Short-haul: roughly one to three months ahead.
• Long-haul: roughly two to six months ahead.
• Peak season, school holidays, Christmas, major events: earlier, because demand fills the cheap buckets long before the curve would normally bottom out.

Last-minute bargains on scheduled flights are largely a myth. They existed when airlines dumped unsold seats; modern revenue management raises prices as departure approaches because the people still buying are business travellers who have no choice.

3. Fly on the unpopular days

Tuesday and Wednesday departures are typically cheaper than Friday and Sunday, because leisure travellers want long weekends and business travellers want Monday mornings and Thursday evenings. Early-morning and late-night departures are cheaper for the same reason.

The old advice to book on a Tuesday is obsolete - airlines now reprice continuously with algorithms. It is the day you fly that matters, not the day you buy.

4. Check nearby airports and split the journey

Most search engines let you add a radius around your origin and destination. A secondary airport an hour away can be dramatically cheaper, particularly where a low-cost carrier operates.

Two related techniques:

• Positioning flights. Fly cheaply to a big hub, then take a separate long-haul ticket from there. Common when your local airport has poor long-haul competition.
• Open-jaw and multi-city. Flying into one city and out of another is often the same price as a return, and saves you backtracking. Always price it before assuming a return is cheaper.

The critical warning: two separate tickets are two separate contracts. If the first is delayed and you miss the second, no airline owes you anything. Leave at least four hours between separate tickets on short-haul and a full overnight on long-haul, and never check a bag through on a self-connection unless the airlines have an agreement.

5. Compare the true total, not the headline fare

A low-cost fare with cabin bag, seat selection, checked luggage and airport transfer added can end up costing more than the full-service ticket that included all of it. Before comparing two options, add:

• Baggage, including cabin bags - several carriers now charge for anything larger than a rucksack under the seat.
• Seat selection, if you care about sitting with the people you are travelling with.
• Payment-method fees, which some airlines still apply.
• Transport from a distant secondary airport, and whether it runs at your arrival time.
• The cost of an overnight if the connection forces one.

6. Consider one long stopover instead of a fast connection

Several national carriers price a long stopover at their hub the same as a short one, and some run free or heavily discounted stopover programmes. It turns a connection you were going to endure into an extra destination, and it is frequently the cheapest routing anyway.

7. Set alerts and let the search run in the background

Rather than checking daily, set a price alert on the route and let it tell you. Most flight search engines do this free by email. It removes the temptation to refresh, and it catches the short-lived drops that happen when an airline releases a new fare bucket or launches a sale.

Sales genuinely exist and are usually announced in January and September, when demand is lowest.

Things that do not work

• Clearing cookies or using incognito. This has been tested repeatedly and does not lower fares. Prices change because inventory changes, not because a site recognises you. Incognito costs nothing, so use it if it makes you feel better, but do not expect a discount.
• Using a VPN to appear in a poorer country. Point-of-sale pricing exists, but the currency, payment card and residency checks usually undo it, and some airlines cancel tickets bought this way.
• Waiting for a last-minute crash. See above.
• Booking on a specific day of the week. Obsolete.

Hidden-city ticketing: why we do not recommend it

The technique - booking A→B→C and getting off at B because it is cheaper than A→B - works, and it is also a breach of nearly every airline's conditions of carriage. Consequences range from having the rest of your itinerary cancelled to losing a frequent flyer account. It also only works one way with hand luggage only. Know that it exists; understand the risk before using it.

Book direct with the airline where you can

Third-party agents are sometimes genuinely cheaper, and occasionally significantly so. But when something goes wrong - a schedule change, a cancellation, a missed connection - the airline will tell you to talk to the agent, and the agent will be slower and less able to help. If the saving is small, book direct. If the saving is large, take it with your eyes open.

Whatever you do, buy with a card that offers chargeback protection, and check that the agent is a real, contactable business before entering card details.

Know what you are owed when it goes wrong

Passenger rights vary by jurisdiction and are worth knowing before you need them. In the European Union and the United Kingdom, long delays and cancellations within the airline's control can entitle you to fixed cash compensation as well as meals, accommodation and re-routing - and that applies to flights departing those regions on any airline, and arriving on their carriers. Rules elsewhere are generally weaker.

Two habits pay for themselves: keep your boarding passes, and photograph the departure board showing the delay.

A simple routine that works

1. Search a whole month, not a date, and note the three cheapest days.
2. Widen the search to nearby airports at both ends.
3. Set a price alert and wait, rather than watching.
4. When a fare appears that is clearly below the running average, book it. Do not try to time the exact bottom.
5. Before paying, add baggage and transfers and compare the true total against one full-service option.

Do that and you will beat most people on your flight, without spending your evenings hunting.