Customer churn is a really interesting problem. It appears to be a simple calculation, but the more you explore it the more complex it becomes. Evidence of this complexity appears in the variety of articles written on the subject, such as:
For Entrepreneurs uses a very straightforward method of calculation, which is then used as the basis for a number of other important SaaS metrics.
Chaotic Flow‘s SaaS metrics archive presents some very interesting questions.
HubSpot expands the subject of churn rate into an entire e-book.
Shopify has a great article on the complexities of calculating churn.
One of the best ways to understand a problem is to create a mathematical model of how it works.
The question we need to answer is: “What exactly is Churn?”