How the grade works
Where the data comes from
Every figure on this site is counted from the US Bureau of Transportation Statistics' Reporting Carrier On-Time Performance file. US airlines above a revenue threshold are required by law to report every domestic flight they operate: scheduled and actual departure and arrival times, cancellations, diversions, and how many minutes of any delay fell into each of five official causes. The file is public domain. We add no estimates and no survey data.
Because reporting is required only of larger carriers, small regional operators, charters and every international carrier are absent from the record. A route flown only by a non-reporting carrier will not appear here at all.
What "on time" means
The federal definition: a flight arrived on time if it reached the gate within 15 minutes of its scheduled arrival. A flight fourteen minutes late counts as on time; one sixteen minutes late does not. Cancelled and diverted flights are excluded from the on-time rate — they cannot be late — and counted separately.
The score
Each airline, route and airport gets a score out of 100:
score = on-time rate − (2 × cancellation rate)
Cancellations are weighted double because they are a worse outcome for a traveller than a delay. A late flight still gets you there; a cancelled one leaves you to rebook, and often overnight. Weighting them equally would let a carrier with a good on-time rate and a bad cancellation habit score as if nothing were wrong.
Letters are cut on the distribution, not on fixed numbers
A, B, C, D and F are assigned by percentile within the period: roughly the top 10% of scores get an A and the bottom 10% an F. That means a grade is always relative to what the industry actually did that year, not to a threshold chosen once and left to drift. In a bad year for the whole industry, an A still marks the operators who handled it best.
Nothing is graded on too little data
An on-time rate calculated from thirty flights is noise. Minimum sample sizes:
- Route: 200 flights in the period
- Airline on a specific route: 100 flights
- Airline overall: 2,000 flights
- Airport: 2,000 departures
Below those thresholds the page still shows the figures as recorded, but the grade is left blank and marked as such. We would rather show a dash than a letter we cannot defend.
What a grade is not
A grade describes the past. It is not a prediction about any particular flight — most delays come from weather, air traffic control and knock-on effects from the aircraft's earlier legs that day, none of which a historical rate can foresee.
It is also not a safety rating. Nothing in this data measures safety, and nothing on this site should be read as saying one airline is safer than another.
Finally, it is not travel advice. AirlineGrades is independent, is not affiliated with any airline, airport or government agency, and takes no payment for placement in any ranking.