What we count
A connection is a time budget. The schedule gives you a number of minutes between one flight landing and the next one leaving. We subtract what actually uses that time.
- Getting off the aircraft. A regional jet empties in a few minutes. A widebody can take twenty.
- Getting to the gate. Same concourse, another terminal, a train or a bus, or out through the exit and back through security. We use each airport's terminal layout and which terminal each airline uses there.
- The boarding cut-off. Airlines close the flight 10 to 30 minutes before departure, depending on the airline.
What's left is your margin on a normal day.
Delays
For every flight we have the last year of arrival and departure records from the US Department of Transportation. We replay the connection across those days, using the same day for both flights. That matters. When a hub has a bad afternoon, your first flight is late and so is your second, and the second one often waits for you. Treating the two as unrelated would make many connections look worse than they are.
Each replay either makes the connection or misses it. If it misses, we look at how long until the next flight to your destination. Missing a connection with hourly service costs you an hour. Missing the last flight of the day costs you the night.
The letters
- AComfortable. Plenty of margin, even with a typical delay on the first flight.
- BGood. Fine unless your first flight is badly delayed.
- CWorkable. Keep moving. Not much room for a bad day.
- DTight. A small delay on the first flight can cost you this connection.
- FRisky. Likely to miss, even without a delay.
We check the grades against what actually happened on past flights. Across 540,000 connections, A grades were missed about 5% of the time, B 10%, C 17%, D 28% and F 32%. "Missed" here means the real delays that day ate the transfer time, since airlines don't publish which passengers missed.
Direct flights
A direct flight gets a grade too, worked out the same way from its own record: how late it usually lands, how often it's more than an hour late, and how often it's cancelled. An A is a flight that's reliably on time. An F is one that's often late or cancelled.
What the grade doesn't know
- Next season's timetable. The flights and times you see are the past year's schedules. A date months away shows last year's routings, which airlines do change.
- Your gate. Gates are assigned on the day, so we use the terminal your airline normally uses at that airport.
- Checked bags, separate tickets, or an international arrival. Each adds a step the grade doesn't include.
- Today's weather. The grade is built on a normal day. On a stormy afternoon, treat every grade as one step worse.
Where the data comes from
Flight records: US Department of Transportation, Bureau of Transportation Statistics. October 2025 to July 2026, 3.6 million flights, 98 airports. Terminal layouts and which airline uses which terminal: the airports' and airlines' own published information. Boarding cut-offs: each airline's published rules.
Grades are estimates, not guarantees. Always check your airline's minimum connection time.