Churn is the rate at which customers leave over a period. It is the number that decides whether your growth compounds or whether you are refilling a bucket with a hole in it.

How to calculate it

Customer churn is customers lost in a period divided by customers at the start of that period. Twenty customers at the start of the month, one gone by the end, and monthly churn is five percent.

Revenue churn measures money instead of logos, and the two can point in opposite directions. Losing five small accounts and keeping the large one looks terrible on customer churn and barely registers on revenue. Losing the large one looks fine on customer churn and takes the quarter with it. Track both, and know which one your business actually runs on.

Net revenue churn subtracts expansion from existing customers. When accounts grow faster than others leave, net churn is negative, and revenue increases without a single new customer. That is the strongest position a subscription business can hold.

Why it compounds

Five percent monthly churn means the average customer stays twenty months. Three percent means thirty-three months. That difference multiplies through everything downstream: what you can afford to pay for a customer, how long before they are profitable, and what the business is worth when someone values it on recurring revenue.

It also caps growth. At five percent monthly churn on a hundred customers, you lose five a month, so five new customers a month is a treadmill. The larger you get, the more you lose in absolute terms, which is why high-churn businesses plateau and cannot explain why.

Reading it honestly

Churn usually reports a decision made much earlier — who you sold to, what you promised, what the first thirty days looked like. Customers who were a poor fit leave on schedule, and no amount of attention in month eleven changes that.

Cancellations also lag. Someone stops using the product months before they stop paying, so a clean retention number can be hiding an empty account that has simply not been reviewed yet.