# Average Time calculations not making sense to me

How are the 7-day Departure Time Averages calculated? Is the time based on previous full week? I’m assuming I have been out of school long enough that my math is rusty because I keep getting a different time than your website when doing the math myself? And by the way, I know this is a complete waste of time on my part but it’s bugging me that I can’t figure it out.

For instance, take DAL871:
http://flightaware.com/live/flight/DAL871/history/20111213/1210Z/KJAN/KATL

As of today (12/13/2011) DAL871 has a 7-day departure Average of 6:20am. I tried calculating that avg two ways: (1) including today and (2) skipping today and beginning 12/12. My calculations come out to 6:17am (rounded up) for today and 6:15am (rounded up) as of yesterday.

Here is my math including today (all minutes were converted to decimal).
0.316666667 (Dec 13)
0.05 (Dec 12)
0.083333333 (Dec 11)
0.466666667 (Dec 10)
0.133333333 (Dec 9)
0.566666667 (Dec 8 )
0.35 (Dec 7)

1.966666667 / 7 = .281 * 60 = 16.85714 or 6:17am

Explanation of sum from above:
(SUM numbers from Dec 13th to 7th) divided by 7 days = Answer multiplied by 60 (convert back to minutes) = average departure time in minutes

I wouldn’t put too much stock into the average departure time.
For one thing, it shows a gate departure time of 06:10 and a take-off time of 06:10.
Another thing: the figure seems to be for the current 7 day period. I went back a few flights and the time never changed. I entered the departure time for the last 7 days (including today) in Excel, averaged the times, and came up with 06:14

06:19
06:03
06:05
06:28
06:08
06:34
06:21
average: 06:14
FlightAware’s average: 06:20

I think they’re over 14 days rather than 7.

Slightly off topic, but how does FA determine when to display the 7 day average? SWA583 does not have a 7 day average?

I see the 7 day average on flightaware.com/live/flight/SWA583

It requires there to be 7 days of flight history, so right after a route change we won’t have it for a few days. But multi-segment direct flights like Southwest likes to do should be fine.