Churn is probably one of the most contentious metrics available to business owners (if you can even imagine such a thing).
While Churn is probably the single most important metric you should be measuring if you sell subscription-based products, it also has no formal definition. In fact, Netflix was sued in 2004 by shareholders, when they accused Netflix of reporting an artificially low churn rate using:
Number of Customers churn / (Number of customers at beginning + number of customers gained)
Where the plaintiffs preferred:
Number of Customers churn / (Number of customers at beginning + number of customers at end of period)/2.
Netflix succeeded in having the suit dismissed, since there is no official way to calculate churn.
