SaaS METRIC OF THE WEEK: Renewal rate
You have to scroll down this articlebefore you get to the informative bit on how to measure this metric but don't because I could just link you to this one). So read the first part anyway: Don't be a jerk when it comes to renewals. If you have to be, maybe it's you, not your customers (keep scrolling again to see the 5 main reasons why people unsubscribe). The difference between retention and renewals is described more in this comprehensive Profitwell article on Renewal Rates.