Cookie Retention Study Reveals Important Data

Really interesting results of a study on cookie retention have been published in one of the Sun Microsystems blogs yesterday. In his “Web Analytics Analyzed” blog Paul Strupp has revealed the following chart which demonstrates “what percent of users returning after X days on the same computer still have the same cookie”:

Cookie retention rates chart

The key numbers/findings of this study reveal:

  • “Very sharp drop” (to 72%) just 7 days after the initial visit
  • 50% of cookies deleted by day 45
  • 360 days past the initial visit the rate “levels out at around 20%”

The above data shows that the majority of Internet users who delete cookies do so within the first 30 days. Starting from day 60 the rate of decay acquires a more gradual character, dropping 45% to 40% between days 60 and 120, then from 40% to 30% from day 120 to 210, and from 30% to about 20% between days 210 and 360.

This study has immediate implications for the context of affiliate marketing. It helps merchants answer the question of  a fair cookie life to set; and it also makes affiliates better equipped for determining which merchants to partner with based on the cookie life they offer through their affiliate programs.

7 thoughts on “Cookie Retention Study Reveals Important Data”

  1. Wow, this is an eye opener for me in many respects. Amazon with it’s 24 hours cookie life used to be the least attractive affiliate program for me, but maybe they are correct after all.

  2. Thank you for your comment, Vlad.

    Upon a closer look at the chart (you can save a bigger image from Paul’s original post), it appears that by the end of that first day, the percentage drops from 100% to about 84%.

    It is also important to remember that the metric which is absent from this study (simply because it wasn’t the subject of it) is timing of affiliate-referred purchases. For example, here’s the data I’ve just pulled for one of my clients’ affiliate programs:


    Average Sale Amounts:

    Same Day: $60.37
    1-2 Days: $47.43
    3-5 Days: $61.74
    5-15 Days: $71.02
    Rest: $56.16

  3. In our tracking systems (we use both PostAffiliatePro and an in-house tracker) we use Flash cookies which not a lot of people know how to delete, in combination with visitor cookie and IP tracking. This helps us keep the affiliate sale attribution accurate even when the HTTP cookie is deleted.

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