Definition: CTOR [Click-To-Open Rate]

CTOR is the acronym for Click-To-Open Rate. It is used to calculate the percentage of people who opened an email, who then went on to click a link within it. CTOR is a useful measure of how interesting the content of an email is, specifically in relation to the subject line and preview text of that email.

CTOR is often used as the CTR of email marketing, however, this comparison is not quite right for many reasons. The most important two reasons are:

  1. CTOR is the result of clicks on any link in an email, meaning it is essentially many CTRs combined.
  2. People who have opened an email are already ‘open’ to the message within the email. This makes CTORs generally much higher than CTRs on other types of digital marketing.

Note: Opens are specified, as it could instead be Click-To-Delivered Rate (for example). By using Opens, the Click-To-Open Rate is examining whether anyone who had the chance to click, did in fact click.



CTOR Formula

This is the Click-To-Open Rate Equation:

CTOR EquationClick to enlarge

Click-To-Open Rate = Total Clicked x 100 ÷ Total Opens


Technical Information

Since the iOS15 update, Apple Mail opens all emails and also removes the tracking on all link clicks from emails. This has a doubly negative effect on CTOR as it increases the opens, but also reduces the attributed clicks.

Apple Mail has a market share of about 12%, so while the effects may be limited it is likely you will notice them in your results.


7 Ideas & Facts About CTOR

  1. Click-To-Open Rate is a way to measure how interested people are in the content of an email (in relation to the subject line and preview text).
  2. CTORs take into account any unique click on *any* link within an email, meaning it is essentially many CTRs combined.
  3. When someone clicks a link in an email, they must have already opened that email! This means they have already shown interest in the email, and this is why CTORs are often so high.
  4. As Click-To-Open Rate is related to the number of times an email is opened, a low Open Rate can inflate your CTOR. Due to this you always need to monitor Open Rate and CTOR together.
  5. While clicks are nice, conversions are always more important. Conversion Rate is, therefore, a much better measure than Click-To_Open Rate for success.
  6. CTR counts all clicks. CTOR counts all clickers (as in people who have clicked – not multiple clicks per person).
  7. Smaller batches of emails often have higher Click-To-Open Rates as they can be more targeted and personalised.


Other Names for CTOR (synonyms)

Clicks per unique opens



CTOR Definition

Glossary Index