How we know: Sources are listed at the end. Feature descriptions come from each product's own help pages. This post contains no price comparisons between the engines: Wildly has not run a head-to-head fare test, and any site that tells you one engine is "cheaper by X%" is describing a snapshot, not a rule.
No single flight search engine sees every fare. Each one has different airline feeds, different refresh timing and different rules about which online travel agencies (OTAs) it will show, so the cheapest result for the same trip can differ between them at the same moment. The practical answer to "which is best" is a division of labour: use Google Flights for dates, Skyscanner for coverage and destination discovery, Kayak for split tickets and a forecast, and Kiwi.com only when you knowingly want a self-transfer itinerary.
Quick comparison
| | Google Flights | Kayak | Skyscanner | Kiwi.com | |---|---|---|---|---| | Type | Metasearch | Metasearch | Metasearch | OTA (sells tickets) | | Flexible-date view | Calendar grid and price graph | Flexible dates option | Whole month / cheapest month | Limited | | Anywhere search | Explore map | Explore | "Everywhere" destination | Yes | | Split or self-transfer tickets | No | Hacker Fares (two one-ways) | Shows some self-transfer itineraries | Core feature (virtual interlining) | | Price alerts | Email when price changes significantly | Daily digest; real-time on roughly 10% moves | Yes | Yes | | Price prediction | Price insights (likely to rise) | Seven-day Price Forecast | No | No | | Where you book | Airline or OTA | Airline or OTA | Airline or one of ~1,200 partners | Kiwi.com itself |
Details and sources for each row are below.
Google Flights
Strengths. The calendar grid and price graph make it the fastest way to find the cheap days in a month, and the Explore map answers "where can I go for this budget" visually. Results load quickly and the interface is uncluttered. Multi-city searches are straightforward.
Price tracking. Per Google's help page, tracking a route emails you when the price "changes significantly"; with "any dates" tracking you get an email when the route's minimum price drops significantly over a month, plus periodic roundups. Google also sends price insights when it estimates fares are likely to rise, with a confidence level.
Limits. Google is a metasearch tool, not a seller; you complete the booking on the airline or OTA site. Coverage of some small low-cost carriers is thinner than Skyscanner's, and alerts are a digest rather than a threshold you set.
Kayak
Strengths. Kayak's filters are granular (layover airport, alliance, aircraft type, time windows). Its distinguishing features, per Kayak's pricing help page:
- Hacker Fares combine "two separate one-way tickets (often from different airlines) instead of a traditional round-trip booking". Useful when one-ways on two carriers undercut a round trip, but you hold two tickets, so a delay on the outbound does not oblige the second airline to help you. (Outbound and return on separate tickets is lower risk than a connection on separate tickets, because there is no same-day dependency.)
- Price Forecast predicts whether a fare will rise or fall "over the next seven days" with a confidence level. Treat it as one input; it is a model, not a promise.
- Price Alerts are mostly sent once a day as a bundled email, with real-time alerts when a price moves roughly 10%.
Limits. The results page carries sponsored placements and partner offers, so the cheapest fare is not always the first thing you see. Alerts cannot be set to a specific target price.
Skyscanner
Strengths. Skyscanner is a metasearch engine that "does not directly sell tickets"; booking is handled by one of about 1,200 partners, according to Wikipedia's entry on Skyscanner. It is well known for the "Everywhere" destination search, which lists every destination from your origin ranked by price, and for the whole-month and cheapest-month views. Its breadth of partners means it often surfaces regional and low-cost carriers, and OTA fares, that other engines omit. It is owned by Trip.com Group.
Limits. The partner model is also the main risk. A fare shown on Skyscanner may be sold by a third-party OTA you have never heard of, sometimes with fees added at checkout and with customer service you will depend on if the flight is changed or cancelled. When the difference is small, book directly with the airline instead.
Kiwi.com
What it is. Kiwi.com is an OTA, not a metasearch site: you buy from Kiwi. Its distinguishing feature is the self-transfer itinerary, which "makes travel cheaper by combining separate flights into unique itineraries", as Kiwi's self-transfer help article puts it. The same article is explicit about the catch: "This isn't an official itinerary offered by the airlines and they won't take responsibility for the unofficial connections." With checked bags you collect and re-check them between flights, and you may have to pass immigration at the connection point, which means you need any visa that country requires.
Protection. Kiwi's own disruption and connection protection, described on its Guarantee help page, covers a missed self-transfer when an airline delays or cancels a flight, and is offered as an optional add-on at booking. Read the terms before relying on it: the rebooking is on Kiwi's timeline, not the airline's.
When it makes sense. Short-haul trips on European low-cost carriers, carry-on only, with generous connection times and no fixed commitments on arrival. It makes much less sense for a long-haul trip with checked bags or a tight schedule.
A five-minute search routine
- Google Flights first. Use the calendar to find the cheapest days around your dates, and note the lowest price and airline.
- Skyscanner second. Search the same dates to see whether a carrier or OTA that Google does not show is cheaper. If it is an OTA, check who the seller is before you get excited.
- Kayak third. Look for a Hacker Fare and glance at the forecast.
- Kiwi.com only if you want a self-transfer routing and accept the risks above.
- Book direct where the difference is small. The airline's own site gives you the simplest path to changes, refunds and rebooking when things go wrong.
For the broader method, see how to find cheap flights.
Why an alert beats repeating the routine
A manual search is a snapshot; fares move as airlines adjust inventory. All four engines offer some kind of alert, and the differences are in cadence and control: Google and Kayak email digests when prices move significantly, Skyscanner and Kiwi notify on change. Wildly checks prices daily on the routes you track and emails you when the fare drops below the target you set, which is the missing piece if you want a specific number rather than a "significant change". Set a price alert on a route such as New York to Paris, Los Angeles to Tokyo or San Francisco to London, then use the engines above when it fires. Our price alerts vs manual searching post goes deeper on the trade-off.
FAQ
Which flight search engine is the cheapest? None consistently. They pull from overlapping but different sets of airlines and agencies, so the cheapest one changes by route and by the hour. Check two or three.
Is Google Flights always accurate? Prices shown are from the airline or OTA feeds at the time of search; you confirm the final price on the seller's site. Occasionally a fare disappears between the search result and checkout.
Is Kiwi.com safe to book with? Kiwi is a legitimate company, but self-transfer itineraries carry risks the airlines will not cover. Read Kiwi's own help pages on self-transfers and its Guarantee before booking, allow long connections, and travel carry-on only if you can.
Should I book through an OTA if it is cheaper? For a small saving, no; you give up the airline's direct customer service. For a large saving from a well-known agency, it can be reasonable. Check the OTA's change and refund policy first.