List churn measures subscriber attrition — unsubscribes, hard bounces, and spam complaints — relative to list size over a period. The formula: (Unsubscribes + Hard Bounces + Spam Complaints) ÷ Starting List Size × 100 per month. Healthy creator newsletters see 0.5–2% monthly churn. High churn (3%+) is a signal that something is structurally wrong with the content-audience fit, sending frequency, or list acquisition quality. Churn has distinct causes that require different responses. Content-audience mismatch is the most common cause in growing newsletters: subscribers joined for a specific value proposition and the content has evolved away from it. The fix is either returning to core positioning or segmenting the list to deliver different content to different audience subsets. Over-mailing causes incremental churn that compounds — subscribers who would stay at two sends per week leave at five. Frequency should be calibrated to the genuine information density you can maintain, not pushed for algorithmic reasons. Poor list acquisition quality creates churn from the start: subscribers acquired through contests, barter, or purchased lists have no genuine interest in the content and unsubscribe quickly. The economic impact of churn is significant and underappreciated. A 2% monthly churn on a 10,000-person list removes 200 subscribers per month — 2,400 per year. At $12 annual subscription revenue per subscriber, that's $28,800 in lost annual revenue that must be replaced just to stand still. This is why reducing churn by even 0.5% per month (preventing 50 unsubscribes per month) is often more economically valuable than accelerating acquisition. Track net list growth: new subscribers minus churn, by month, to understand whether your list is genuinely growing or running in place. The most effective churn reduction tactic is proactive re-engagement before subscribers mentally check out. A re-engagement email sent to subscribers who haven't opened in 60 days, asking directly whether they still want to receive the newsletter, performs three functions: it recovers 5–15% of dormant subscribers who reconfirm, it cleanly removes uninterested subscribers before they become complaints, and it signals to ISPs that you're actively managing engagement — improving inbox placement for your active list. Run re-engagement campaigns quarterly on lists above 2,000 subscribers. The metric to watch after a re-engagement sweep is not just how many subscribers remain — it's whether open rate increases on subsequent sends. A 10% smaller list that opens at 45% rather than 28% is more valuable to sponsors, generates higher eCPM, and has better deliverability than the unclean version.