Leave at your original time. A posted delay moves an estimate, and the airline can still board on the original schedule. When the plane arriving for your flight ran 10 to 19 minutes late, 27% of the next flights still left at or before the scheduled time, and 38% left within 5 minutes of it.
The delay on the board is a guess at the time it was typed. The check-in and bag cutoffs still count from the scheduled time. And a wrong call costs far more in one direction than the other: arrive 20 minutes early and you read a book, arrive 20 minutes late and you may have missed it.
What happens to a slightly late plane
I followed each aircraft from one flight to its next through public flight records, for about 7 million US domestic flights over the 12 months to August 2026. The inbound’s lateness is the closest public stand-in for the small delays people see posted, since records can’t show what a board said at any given moment.
| Inbound arrived | Median departure of the next flight | Left at or before schedule | Left within 5 min |
|---|---|---|---|
| 1 to 9 min late | 1 min late | 48% | 63% |
| 10 to 19 min late | 10 min late | 27% | 38% |
| 20 to 29 min late | 19 min late | 17% | 23% |
| 30 to 44 min late | 31 min late | 12% | 16% |
A 20-minute delay still left about one flight in six on the original time. Those are mostly flights with room in the turn, which brings up the number that decides this: how long the plane was scheduled to sit on the ground.
Here’s a plane 10 to 19 minutes late, by its scheduled time at the gate.
| Scheduled time at the gate | Median departure | Left at or before schedule | Left within 5 min |
|---|---|---|---|
| Under 45 min | 18 min late | 4% | 12% |
| 45 to 59 min | 12 min late | 17% | 29% |
| 60 to 89 min | 4 min late | 38% | 53% |
| 90 min or more | 3 min early | 68% | 78% |
With a long turn, a small delay disappears. That’s why the board can read “10 minutes late” and the flight can board on time anyway.
The deadlines don’t float
Cutoffs follow the scheduled departure unless the airline says otherwise. JetBlue’s page puts it directly: miss the international check-in deadline and you may be denied boarding, even if the flight is delayed. Southwest’s contract allows it to depart early when everyone who met the check-in rules is on board. Delta’s says it won’t hold a flight for passengers who aren’t at the gate on time.
The DOT also warns about the opposite problem. It calls it a “creeping delay”: the estimate gets longer as the morning goes on, because weather that should have improved didn’t, or a repair turned out to be harder. It says early estimates are sometimes hard to make. Either way, the first number you see isn’t the last.
When you can change your plans
Moving your leave time makes sense in a narrow set of cases, and all of them involve evidence stronger than a number on a board.
The flight is cancelled. Don’t go, and deal with the rebooking from wherever you are.
The airline has told you, in plain words, to come later. A new estimate on a screen isn’t that. A message saying you can arrive later is, and even then keep the original bag cutoff in mind unless it says otherwise.
The plane is a long way off. If the aircraft for your 2 PM flight hasn’t left Denver, and it’s two hours from you, then physics has a say. Late aircraft shows how to find it, and that a flight usually leaves about 45 minutes after its plane parks. Even then I’d keep some margin, since an airline can swap in a different aircraft that’s already there. That would put you back on the original time.
Everything else, go. If it’s a ground stop for your destination, it can end with no notice. A 10-minute delay on a flight with an hour-long turn is noise.
The airport isn’t a bad place to be wrong. You’d have some time near the gate, and leaving on schedule means your margin survives if security is slow too.
An inbound isn’t a posted delay
A flight can be posted late for reasons that have nothing to do with its plane: crew, a gate, weather where you’re going. Those aren’t in these tables, and I can’t show how often a posted delay held. What I can show is how much a small delay on the aircraft side carries through. Airlines may also handle one flight differently from another. Records are gate times for domestic flights, by large US airlines and their regional partners, where one aircraft flew both legs within six hours, and they leave out cancelled and diverted flights.
The airline’s app outranks all of this. Check it before you change anything.
When your flight runs late, Skycap says by how much, and the leave-by stays on the airline’s schedule. It tells you the airline can still board on the original time, so check its app before you change plans. How the leave-by works