How accurate are departure times for airplanes? If the departure time is 9:30 and I come at 9:45 will I be able to board?

No, barring the fact most airlines close the doors to board at no later than 10 minutes before departure, even a delayed flight would probably see you staring at the plane taxiing to the runway as you look out of the terminal window.

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Only if you can run very fast and fly. Even if you catch up with the aircraft the captain isn't going to open the door and let you in, something to do with cabin pressure.

From what I've been hearing, you need to get there at 7:30 to be able to board by 9:30.

Definitely not.

The airport gate would likely be needed for a next flight, and unless it was delayed from the get go, at 9:30, the door would have been closed and the aircraft pushed away from the gate.

Departure time means when they pull away from the gate. You will have to run like a bastard to get out to the taxiway

Unless there a delay it will leave at 9:30. All the airports work together to get flights in and out as quickly as possible. If you can only get there at 9:45 count on it being gone. Make other arrangements.

Airlines hope to close the doors 10 minutes before scheduled departure, or the announced departure time if delayed. If you arrive at the gate at 9:25 for a 9:30 flight you may not be able to board.

The chances of your flight being delayed varies with the time of day, the airport, the weather, and the airline. The earlier in the day, the less likely it is to see a delay. If you look travel sites they often give the on time percentage for a given flight, but it's rare to see a flight that is delayed even half the time.

Seriously? By 9:45 the airline will no long be allowing any passengers to board. In fact, it might already be long gone.

If you are not there by 9:15 your can start making other travel arrangements.

Unless there is an announced delay, you should be at the boarding gate at least 30 minutes before departure. The boarding gate will close 10-15 minutes before departure and will not be opened, even if the plane is still there when you arrive. If you arrive 15 min after the departure time, there's a good chance your plane will be gone.

Barring any weather or mechanical issues, airlines usually pull out on time. If you show up AFTER the departed time, you are SOL.

Actually they board about 30 minutes before the scheduled departure time and generally close the door 15 minutes before departure. Then the pull away from the gate at the scheduled time. If you show up 15 minutes after the scheduled time, you will likely see an empty gate.

Nope
Boarding ends 15 minutes before scheduled departure time
Even if the plane was delayed if you arrived at 9:45 for a 9:30 flight you will not be allowed to board

You can do what this couple does:

https://www.youtube.com/watch?v=Bk_G1Df0_qg

They are very accurate, as a rule. If you're not there by 9:20 you've probably missed the flight.

Probably not. MOST commercial flights close boarding several minutes BEFORE departure time to allow passengers and cabin crew to settle in and prepare for the flight. If your flight was scheduled to depart at 9:30, it's likely that the aircraft doors were closed before 9:25. That's why they tell you to arrive at the airport AT LEAST an hour prior to scheduled departure time.

No

They are fairly accurate. They do their best to meet those departure times as one might imagine, they need to have the aircraft at the next destination to meet their next leg times.
Things can cause delay, such as weather or passengers not taking their seats quick enough, which causes the crew to delay closing the door and proceeding with the public address with the safety briefing.

if they don't leave at the posted time then who the hell knows when they're going to leave. maybe you'll be able to board and maybe you won't

if you want to be so damn sure you get on then make sure you get there early instead of late. yeah i know it's a crazy idea

No.