FlyOnSchedule

Methodology: How On-Time Statistics Are Calculated

Data through July 2026 · Last updated October 18, 2026

This page explains exactly how every number on FlyOnSchedule is calculated. All figures come from BTS flight records; nothing is estimated, modelled or filled in.

Definitions

MeasureDefinition
On-time arrivalA flight that arrived less than 15 minutes after its scheduled arrival time (BTS field ArrDel15 = 0). The on-time rate is on-time flights divided by completed flights, which excludes cancelled and diverted flights.
On-time departureA flight that left the gate less than 15 minutes after its scheduled departure time (DepDel15 = 0), out of all flights with a recorded departure. Airport pages use this measure because it reflects what happens at that airport.
Cancellation rateCancelled flights divided by all scheduled flights.
Avg delay when lateThe average arrival delay, in minutes, of flights that arrived 15 or more minutes late.
Avg departure delayThe average difference between actual and scheduled departure for all departed flights. Early departures count as negative.
Delay causesAirlines report the minutes of each delay of 15+ minutes in five categories: carrier (within the airline’s control), weather (extreme weather), NAS (the National Aviation System: air traffic control, non-extreme weather, airport operations), security, and late-arriving aircraft. We show each category’s share of the total minutes.
Departure hourThe scheduled departure time, in local time at the departure airport.
AirlineThe airline that operated the flight, as reported to BTS. Regional airlines such as SkyWest, Envoy, Republic and PSA fly under the brands of larger airlines (for example American Eagle) and have their own pages. The “American Airlines” figures cover only flights operated by American itself.

Time windows

  • Headline numbers, rankings, airline tables and comparisons use the last 12 months: August 2025 to July 2026.
  • “Best time to fly” figures (by hour, day of week, month and holiday period) and monthly trend charts use the last 24 months: August 2024 to July 2026. Using more months gives larger samples.
  • Holiday periods: Thanksgiving week (Tue before to Mon after) (2024-11-26 to 2024-12-02, 2025-11-25 to 2025-12-01); Christmas & New Year (Dec 20 - Jan 3) (2024-12-20 to 2025-01-03, 2025-12-20 to 2026-01-03); Summer peak (Jun 15 - Aug 15) (2024-08-01 to 2024-08-15, 2025-06-15 to 2025-08-15, 2026-06-15 to 2026-07-31). Each is compared with all other days in the same 24 months.

Minimum data rules

Page or figureRule
Airline pageAt least 5,000 flights in the last 12 months.
Airport pageAt least 365 scheduled departures in the last 12 months (about one a day).
Route pageAt least 300 flights in the last 12 months between two large hubs, or 150 when either airport is smaller. A large hub is an airport with at least 1% of all US departures (30 airports).
Any split (hour, day, month, airline on a route)Shown only with at least 30 flights; smaller splits are marked “limited data”. A best or worst departure hour must also cover at least 1% of the flights.

Routes are directional: New York to Los Angeles and Los Angeles to New York are separate pages because their delays differ.

Colour key

On-time badges are green at 80% or more, amber from 70% to 79.9%, and red below 70%. Each colour also has its own shape (circle, diamond, square), so the key doesn’t depend on colour alone.

Data checks

Before publishing, every month of data is checked automatically: the flight count must be in the normal range, flags must be valid, delay minutes must be consistent with the on-time flag, and every airport and airline code must match the official BTS lookup tables. If any check fails, the update stops and the previous version of the site stays live.

MonthFlights in BTS fileReporting airlines
July 2026631,97012
June 2026607,57712
May 2026611,73513
April 2026597,91913
March 2026612,10213
February 2026515,03713
January 2026544,00313
December 2025582,30414
November 2025570,55014
October 2025605,84414
September 2025562,43914
August 2025602,37814
July 2025631,42814
June 2025611,57514
May 2025605,64814
April 2025583,95014
March 2025600,87214
February 2025504,88414
January 2025539,74714
December 2024590,58115
November 2024575,40415
October 2024615,49715
September 2024582,62215
August 2024619,02515