The cost of airplane flights is often the biggest expense of travel. Airfares can be expensive and budgeting for them can be difficult. Prices change often so it is not easy to know which flight is best. And there can be extra charges for baggage.

　　The process is even more complex for family travel.

　　Now, the online search service Google Flights has a new tool to help you find the best airfares and plan your next trip. The service can let you know when the price for a flight is going to end. It can alert you when prices are expected to rise. Google Flights now compares airfares to historical price data for similar flights.

　　Using Google Flight's New Tool

　　To use this new tool, go to the Google Flights website.

　　You can search for flights by date, airports, number of stops, flight class and number of passengers. Google Flights will highlight in green the flights it thinks are the best choices, based on price, flight times and number of stops.

　　After you choose a flight, you may also see a note about when the price is set to end. Google Flights may also suggest you book as soon if prices are expected to rise soon.

　　This tool only works when a flight's historical data is available. The information may be able to show you how much time you have to book a flight before the price changes.

　　Track Prices

　　Search results include a "Track Prices" option. You can turn on to receive emails about price changes and travel tips. Google Flights lets you choose Track Prices even if you have not yet purchased your tickets nor chosen a flight.

　　You can manage your tracked flights and change the search fields, such as number of passengers, airports, dates and more.

　　Google Flights will e-mail you if there is a considerable change in airfares for your saved flights.

　　Comparing Airfares

　　Google Flights also has other tools to help you compare airfares. It provides a calendar with flight prices listed every day. You can see flight prices listed by date so you can choose an economical time to fly.

　　You can also see airfares on a bar graph to compare prices easily.

　　Google Flights also shows airfares on a map to help you decide where to go.

　　You may see a tip at the top of the results, advising that you could save money by flying on a different date or from a nearby airport.