Why does my Feedburner Subscriber Count Fluctuate?

• Why does my Feedburner subscriber count fluctuate so much?
• Are people unsubscribing and subscribing as much as my Feedburner counter says?
• I notice your Feedburner counter goes up and down each day – why?
• My RSS Subscriber Counter Goes Down Every Weekend – Why?

Over the last week I’ve been asked these and similar questions about Feedburner subscriber numbers a total of 7 times. Each time I’ve muddled through an answer to the questioner, thinking I knew the answer but not being sure.

So this morning when I woke to the question twice more in my inbox I thought I’d go straight to the font of all knowledge at Feedburner – Rick Klau (Feedburner’s Vice President of Publisher Services) and ask him for an official explanation of fluctuating Feedburner subscription numbers.

Here’s how Rick answered the question:

When we report a subscriber number, that represents the total number of individuals who had the feed requested on their behalf on that day.

Most of these subscribers fall into one of two groups:

1. those using a stand-alone feed reader
2. those using a web-based feed reader

In the case of stand-alone feed readers, that user has an application running on their computer which fetches the feed repeatedly throughout the day. We look at characteristics of those requests, and differentiate between repeated requests from the same person (as indicated by regular polling intervals, consistent IP addresses, and common user agents) and different requests (where one or more of the previous data points vary).

In the case of web-based feed readers (My Yahoo, Google Reader, Bloglines, Pageflakes, etc.), those services retrieve the feed repeatedly throughout the day, but do so on behalf of multiple people. Almost all of these services report to us how many of their users are subscribed to the feed. At the end of the day, we tally up how many stand-alone feed readers are subscribed, and add them to the web-based users. The end result is the total subscriber number we report. (I’m leaving a few details out; see below for a more complete answer.)

The fluctuations are almost always due to people using stand-alone computers who don’t turn their computer on, or don’t load their feed reader on a given day. If their feed reader doesn’t ask for the feed that day, we don’t see them, and consequently don’t include them as a subscriber. (note from Darren – this is why on weekends numbers tend to go down as a result of less people checking their feed reader).

Other explanations are when a site gets Dugg – large spikes in traffic, at least when some of the visitors are using older versions of browsers, may result in us being unable to differentiate between browser accesses of the feed and the browser’s feed reader accessing the feed. A more detailed explanation of this phenomenon is here – look for my answer to the question asking about spikes from getting Dugg.

Finally, for a more comprehensive look at the various components of a subscriber report, we did a case study last year on TechCrunch. It should provide even more context for the hows and whys of subscriber calculations (and fluctuations). It also makes some important comments on “Reach”. Unlike the subscriber number, which may be representative of people who indicated an interest in your content but who do not actually read it, Reach reports on just the items that were viewed in aggregators or the clicks that drove traffic back to the publisher’s site. As a result, it represents a much more accurate picture of the engagement a feed’s audience enjoys, while the subscriber number represents the total audience who’s expressed an interest in the content.