I'm looking into how useful returning visitors stats in Google Analytics are over longer periods of time, such as two or three years.

It seems that the __utma cookie is set to expire 2 years from set/update, so this suggests that this cookie should be updated each time the user visits the site, and the 2 year expiration reset.

Would I be right in thinking then that it's reasonable to expect the returning visitors data to be no less accurate over longer periods than it is in the last year, for example?

  • Can you clarify the last sentence?
    – dan
    Commented Jan 21, 2014 at 1:35
  • What I was trying to ask is just if I'm understanding the cookie timescales correctly, and if this means that returning visitors stats are reliable for longer periods of time, such as going back 2 or 3 or 4 years - hope that makes sense!
    – jawilson
    Commented Jan 21, 2014 at 8:03

1 Answer 1


When you are talking about the timescale of years, the data won't be very accurate. Cookie expiration is not even the main reason. Over the course of two years I would expect a large number of visitors to lose their cookies altogether for reasons such as:

  • Clearing the cookies manually
  • Switching browsers
  • Using your site on a different device (phone, tablet, home computer, work computer)
  • Reinstalling the operating system or factory resetting a phone or tablet
  • Buying a new computer, phone, or tablet

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