The 15-minute rule
The most widely used definition comes from the US Department of Transportation's reporting rules: a flight is counted as on time if it arrives at the gate less than 15 minutes after its scheduled arrival time. Arriving 14 minutes late is on time; 15 minutes late is a delay. Most airlines, airports and statistics bodies around the world use the same threshold, sometimes applied to departures as well as arrivals, which is why "A14" (arrival within 14 minutes) and "D0" (departure exactly on schedule) appear in industry reports.
Arrival is the measure that matters to passengers, and it is the one regulators publish. Departure punctuality is tracked internally because a late pushback is the leading indicator of a late arrival, but a flight that leaves late and makes up the time en route still counts as on time.
How the times are measured
- Scheduled times are the airline's published timetable, which can change up to the day of travel.
- Actual departure is pushback from the gate, recorded when the parking brake is released ("off-block"). Taxi-out time, waiting for take-off, is not a delay in these statistics.
- Actual arrival is the moment the aircraft stops at the gate ("on-block"), not touchdown. A flight can land on time and still be delayed if it waits for a gate.
- Some data feeds publish runway times instead of gate times. Taxi-in and taxi-out together typically add 15 to 40 minutes, so comparing a gate time with a runway time will mislead you.
Why schedules are padded
Airlines set schedules using historical block times, and most add a cushion so that typical delays still land inside the 15-minute window. That is why an early arrival is common on a long flight and why the published duration of a route has often grown over the decades even as aircraft got faster. Padding improves the on-time statistic without changing how long you actually sit on the aircraft.
Where delays come from
Regulators sort delays into a few causes: the airline's own operation (crew, maintenance, late-arriving aircraft from the previous flight), extreme weather, the air traffic system (congestion, flow restrictions, routine weather), security, and cancellations or diversions. Late-arriving aircraft is consistently the biggest single category, because one delayed morning flight pushes every later flight on that aircraft's rotation. It is also why early-morning departures are statistically the most punctual: the aircraft has been parked overnight and nothing upstream has gone wrong yet.
Reading a flight's punctuality history
For the flights we follow, each flight page records the scheduled and actual times every day the flight is looked up, and once there are enough observations it shows the average departure delay and the share of arrivals within 15 minutes. A few things to keep in mind when you read it:
- Small samples swing wildly. One diversion in ten observations is a ten-point drop in the on-time rate, so we only show percentages once there are at least ten.
- A flight's number can move between aircraft types or times of day with a schedule change; the history table shows the aircraft that operated each day so you can see that.
- Cancellations do not appear as delays; a cancelled flight simply has no actual times.
- Our observations are snapshots from a flight-data provider, so an actual arrival time is only recorded if the flight had landed when the page was last refreshed.
What to do with the information
If two flights on your route have similar fares, the one with the better on-time history is the better bet, and an early departure is generally safer than an evening one on the same rotation. If you have a tight connection, look at the arrival delay distribution rather than the average: a flight that is usually on time but occasionally two hours late is worse for connections than one that is reliably twenty minutes late.