What's the difference between CTR and CTOR?
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CTR (click-through rate) and CTOR (click-to-open rate) measure two different things about your email performance, and mixing them up leads to bad conclusions.
CTR (click-through rate) = clicks divided by delivered messages (or sometimes by total sends). It measures how many of the people who received your email clicked something. It's a reach metric: out of everyone who got this email, how many took action?
CTOR (click-to-open rate) = clicks divided by opens. It measures how many of the people who opened your email clicked something. It isolates content quality from deliverability and subject line performance.
Here's why the distinction matters: a low CTR could mean your subject line is weak (low opens means fewer chances for clicks) or your content is weak (people opened but didn't click). CTOR separates these. If your CTOR is high but CTR is low, the content is working fine. Your subject line or deliverability is the problem, not the body of the email.
CTOR is the better diagnostic tool. CTR is the better audience-level performance metric.
The caveat with CTOR: since it uses opens as the denominator, it inherits the same reliability problem. Apple MPP inflation artificially increases your open count, which pushes CTOR down. If you're comparing CTOR before and after September 2021, the denominator changed. Post-MPP CTORs look lower than they used to, even for the same content quality. What counts as a good CTOR has shifted as a result.
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