Open Google Flights when you want to see the cheaper day and then watch it. The page says the date grid and price graph make flexible dates easy to scan, and that price insights tell you whether the fare looks like a time to book, based on history. It says tracking notifies you when the price of a route or a flight drops. Another line says you can describe an ideal trip and let Google Flights find deals. Nothing on the page lists a fee. You buy the ticket on the next site. The alert does not freeze the fare.
Open Hopper when you want a book-or-wait signal inside an app, and only after you accept that we could not reload the product page. On October 18 the listing said search is free and that Price Freeze and other protections cost extra, with the fee shown in the booking and changing by trip. On July 2, 2026 the FTC said Hopper agreed to pay $35 million over allegations that fees were charged without clear consent and that Price Freeze and VIP Support were misrepresented. The order was entered August 20, 2026. Read the fee screen. A prediction is not a promise the fare will drop.
Use both only if you keep the jobs apart. Google Flights is the calendar and the notification. Hopper, on the last page we could read, is the prediction and the paid protection. If the currency is points rather than cash, neither page is the award search. Use seats.aero, point.me, or Roame for that.