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How We Count Our Users

We want our count of unique users that the AddThis network sees per month to be one our customers can believe in.  This post explains our methodology for generating that number.

There are 2 numbers to consider:

  • Raw uniques – The raw number is really a count of all cookies, including bots and everything.
  • Good UID – We use a “good UID,” a number that we know is lower than our actual reach, but better to be conservative.


Here’s how we get to our “good” UID:

  • Start with time component:  We start with every cookie that has been seen at least twice over a period greater than 24 hours apart because we need to be sure that we do not include bots and consumers who constantly clear their caches.  The time component is crucial to an accurate count because there are many cases where transient consumers appear in the log files multiple times in a narrow time period but then disapear from the logs a short while later.  A filter that counts any consumer seen multiple times would count this activity incorrectly and cause the unique user count to be inflated.
  • Count Unique Monthly Users: Then we take a de-duplicated count across all of the days in the month we are measuring to get the total count.  As we have discussed in another blog post, this is not a trivial task and it is tempting to take the easy way out and simply sum the total unique users by day in order to get the final unique user count.  Doing so would overestimate the actual number of unique users counted.
  • Consider multiple devices: Unfortunately there is no reasonable way to detect when the same person uses multiple devices to access the internet, this is very common in the US and other westernized countries.  For this reason, we take the floor of our total unique user count to reduce the impact of overcounting multiple devices.


Even with our conservative counting approach, we’re proud to be on sites that reach 1.3B users on a monthly basis, making us the largest social sharing platform on the open web. We’d love your feedback and would be happy to expand on any aspect of our methodology.