https://towardsdatascience.com/whats-a-customer-worth-8daf183f8a4f > In E-Commerce or retail business, the relationship between businesses and customers are non-contractual relationship. In the non-contractual world, customers do go away, but they do so silently; they have no need to tell us they are leaving. This makes for a much trickier CLV calculation. We have to look at the time since a customer’s last transaction and ask a question: is the customer alive but dormant, or is the customer “dead” (“alive” means customers interact with us, “die” means they become inactive as customers)? > So, here we are: modelling customer lifetime value for non-contractual business.