The other day someone asked me an interesting question about Google analytics:

how is average time on site calculated? And if I go on a site and leave it open for several hours won’t that skew the average results?

That is a good question I didn’t know the answer but I knew Google would have a way to avoid this.

Well I’ve done some research and I can now explain how Google Analytics calculates the average time spent on a site. When a visitor first enters a site and goes from one page to another the time on the site is calculated by the elapsed time from the first page to the next (each page visit has a timestamp)

But if a visitor leaves the page open with no activity for a predetermined time (consensus of opinion seems to say this is upto 1 hour or so, but could be a lot less) then the that visitor is marked as an exit and the time spent on the last page is = 0.

This avoids the problems we were talking about leaving the page open and skewing the average. If the visitor then recommences surfing the site several hours later it is recorded as a return.

All bounces are excluded in the average time calculations, again because they would skew the average result.

Google will take the total time on the site and divide by the number of visitors to give the average time spent on the site.

I hope my explanation makes sense?