Click-to-open rate compares the people who clicked with the people who opened. It is calculated as unique clicks divided by unique opens. If 1,000 people open a campaign and 120 click, the CTOR is 12%. Because the subject line has already done its work by the time someone opens, CTOR isolates the content: the layout, the offer and the calls to action.
That makes it handy for diagnosis. A campaign with a strong open rate but weak CTOR suggests the subject line promised something the email didn’t deliver, or that the main link was hard to find. A campaign with a modest open rate but high CTOR suggests the content worked well for the people who saw it, and the subject line or timing deserves attention.
CTOR has a weakness: its denominator is opens, and opens are now inflated for many audiences by Apple Mail Privacy Protection. If a growing share of “opens” are automatic, CTOR falls even though nothing about your content changed. When comparing CTOR over time, check whether your open rate rose suddenly, and prefer comparisons between campaigns sent to similar audiences around the same period.
Use CTOR alongside click-through rate rather than instead of it. CTR tells you how the whole send performed; CTOR tells you whether the content inside earned its clicks. Together with a click map of individual links, they show where to change things in the next email.
A travel agency in Kochi sends a monsoon-trips newsletter. It has a 35% open rate but only a 4% CTOR. The click map shows most readers never reached the packages, which sat below a long introduction. Moving the packages to the top lifts CTOR to 9% on the next issue.
Every MailNesto campaign report includes click-to-open rate next to open and click rates, plus a click map showing the share of clicks on each link.