Click-Through Rate vs Click-to-Open Rate: What's the Difference?

Click-through rate (CTR) is the percentage of total email recipients who clicked a link, calculated against everyone the email was sent to - unique clicks divided by emails sent - regardless of whether they opened the email at all.

Click-to-open rate (CTOR) is the percentage of people who opened the email and then clicked a link, calculated only against unique opens rather than total sends - unique clicks divided by unique opens - filtering out everyone who never opened it in the first place.

Because the two use different denominators, they answer different diagnostic questions about the same campaign. CTR reflects performance across the entire audience, which folds together two separate factors: how many people opened the email, and how many of those openers then clicked. CTOR isolates the second factor alone, showing specifically whether the content, design, and call-to-action actually worked for the people who did see it. Reading both together is what makes a weak result diagnosable: a low CTR paired with a strong CTOR means the open rate is the actual problem - the content clearly works once someone opens it, so the fix belongs on the subject line or send timing. A low CTR paired with a weak CTOR points the other way - people are opening the email at a normal rate, but the content itself isn't landing once they do, which is a copy or design problem rather than a deliverability or subject-line one.