What is subscriber churn?
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You send a campaign, check the numbers a week later, and notice your list is a little smaller than it was before. That's churn at work. Subscriber churn is the rate at which people leave your email list over a given period.
It's not just one thing, though. Churn captures all the ways an audience shrinks. Unsubscribes are the most visible (someone hit the button and opted out). But list decay contributes too. Addresses get abandoned, people stop opening, and some contacts hard bounce because the inbox no longer exists. All of that counts.
A simple way to calculate it: take the number of subscribers you lost in a period, divide by your starting list size, multiply by 100. If you started the month with 10,000 subscribers and ended with 9,700, your monthly churn rate is 3%. That adds up fast over a year.
Why does it matter beyond the raw numbers? Churn affects deliverability. A list that's quietly filling up with inactive or abandoned addresses starts to look bad to mailbox providers. Low engagement signals, rising bounce rates, and occasional spam report risk all trace back to churn that wasn't managed. Sending to a churned-up list can hurt your sender reputation even if the churned contacts haven't complained.
Some churn is inevitable and normal. People change jobs, change interests, change email addresses. The goal isn't zero churn. It's catching the warning signs early and knowing when to take action before a shrinking list becomes a deliverability problem.
If you want to see the shape of your list health right now, our free Blocklist Checker is a good starting point, or drop us a line on the SOS hotline if things feel off.
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