How is CTOR calculated?
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The formula: unique clicks divided by unique opens, multiplied by 100.
So if 1,000 subscribers opened your email and 80 clicked a link, your click-to-open rate is 8%.
Compare that to regular click-through rate, which divides by delivered emails instead of opens. If the same campaign reached 10,000 recipients, the CTR would be 0.8% and the CTOR would be 8%. Both are accurate. They're just measuring different things.
CTOR is most useful when you want to understand how compelling your content was for the people who actually engaged with it. CTR tells you about overall list performance. Use them together to separate "did my subject line land?" from "did my content work once they were inside?"
One thing to factor in: CTOR depends on reliable open data, and Apple Mail Privacy Protection has been inflating open counts since 2021. If machine-triggered opens are in your denominator, your CTOR will look lower than it actually is.
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