Flight Deals from St. Louis to Rome from $501

Flight times and distances come from our flight-schedule database, which combines published airline timetables, U.S. government schedule data from the Bureau of Transportation Statistics (BTS), and observed flight operations from the EUROCONTROL/OpenSky Open Performance Data Initiative (OPDI). The typical flight time is the median scheduled block time across all carriers on the route, computed the same way in both directions so the difference reflects prevailing winds rather than any change in method. Distance is the great-circle distance between the two airports, so the actual flown track is typically 2-5% longer.

Airlines and weekly frequencies are compiled from our flight-schedule database, which combines published airline timetables, U.S. government schedule data from the Bureau of Transportation Statistics (BTS), and observed flight operations from the EUROCONTROL/OpenSky Open Performance Data Initiative (OPDI). We count each operating carrier's scheduled weekly departures and the days it flies; where there is no nonstop service, connecting carriers are identified by linking scheduled nonstop segments through common hub airports. Where a median fare is shown for a carrier, it reflects the real fares Priceline users found on this route in the last 72 hours.

Seasonal fares come from Priceline's own air booking-summary archive, analysed in-house and refreshed monthly. For each day of the year we take a representative round-trip fare, a blend of the 25th-percentile and average ticket price over the route's bookings, and smooth the series into a seasonal curve; the half-month low and high and the monthly figures quoted here are averages of that curve. Thin and international routes borrow their seasonal shape from the nearest busy routes, with the price level anchored to the route's own bookings.

Booking-window guidance comes from the same monthly in-house analysis of Priceline's own air booking-summary archive. We aggregate the route's bookings by how many days before departure they were made, from about 180 days out to the day of travel, smooth the curve, and highlight the stretch of lead times with the lowest average fare. Thin and international routes borrow the curve shape from the nearest busy routes, anchored to the route's own price level. It reflects current fares and is refreshed monthly.

Red-eye flights are identified from scheduled local departure and arrival times and block times in our flight-schedule database — built from published airline timetables and official schedule data, including U.S. Department of Transportation records for domestic routes. A flight counts as a red-eye when it departs in the afternoon or evening (3 p.m. or later local time) or in the early hours before 4 a.m., and is in the air at some point between midnight and 4 a.m. local time at both its departure airport and its arrival airport. An evening flight that lands before midnight at its destination is never counted, nor is a morning departure or a daytime long-haul that reaches the next calendar date only because of time zones. Each red-eye is labelled with its timing (for example, overnight and landing the next morning, or late-night and landing after midnight). For connecting itineraries the same rule is applied to the longer leg, from one representative day's flight search.

Airlines and weekly frequencies come from our flight-schedule database, which combines published airline timetables, U.S. government schedule data from the Bureau of Transportation Statistics (BTS), and observed flight operations from the EUROCONTROL/OpenSky Open Performance Data Initiative (OPDI). We count each operating carrier's scheduled weekly departures and the days it flies; where there is no nonstop service, connecting carriers are identified by linking scheduled nonstop segments through common hub airports. Where a typical fare is shown for a carrier, it is the median of the real fares Priceline users found on this route in the last 72 hours.

Aircraft types come from our flight-schedule database, which combines published airline timetables, U.S. government schedule data from the Bureau of Transportation Statistics (BTS), and observed flight operations from the EUROCONTROL/OpenSky Open Performance Data Initiative (OPDI). For U.S. routes the type is grounded in the tail number that actually operated the flight; elsewhere it comes from the airline's filed equipment code. Where the source does not commit to a specific variant we name the aircraft family (for example Airbus A320 family) rather than guess, and where no reliable type is on file the aircraft is omitted rather than estimated. Types describe typical scheduled equipment and can vary with seasonal or day-of-week assignments and last-minute swaps.

Airlines and weekly frequencies are compiled from our flight-schedule database, which combines published airline timetables, U.S. government schedule data from the Bureau of Transportation Statistics (BTS), and observed flight operations from the EUROCONTROL/OpenSky Open Performance Data Initiative (OPDI). We count each operating carrier's scheduled weekly departures and the days it flies; where there is no nonstop service, connecting carriers are identified by linking scheduled nonstop segments through common hub airports. Where a median fare is shown for a carrier, it reflects the real fares Priceline users found on this route in the last 72 hours.