Glossary
Call to action
Also called CTA.
Last reviewed 18 September 2026
What is a call to action in an email?
A call to action is the single thing an email asks the reader to do, stated plainly and linked once, which in a course email is usually the step that day’s lesson was teaching rather than a request to buy anything.
One per email is the working rule. A message with three asks is a message with none taken, and in a teaching sequence the ask is also the measurement, because a click on a link that a reader who actually did the thing has a reason to press is the only progress signal worth counting.
Put the link where it belongs in the teaching, on a worksheet, the next step or a reply prompt, rather than at the bottom as a read-more. A course can afford a plain ask: the reader confirmed their address for this, and the sequence is the reason the message is in front of them.
See also
- Click-asserted progress
Click-asserted progress is measuring how far a reader got through a course by acts that required a decision from a person, such as a click on a link in the last lesson, rather than by an open, which is an image load a machine can perform.
- Completion rate
A completion rate is the share of confirmed subscribers who reach the end of a course, and for a five-day course measured by a click on the last day it commonly runs between one in ten and one in four, with longer courses lower.
- Subject line
A subject line is the line an inbox shows beside your name, and the length that matters is not the total but the front of it: put what is interesting in the first 30 to 40 characters, which is roughly what an iPhone held upright will show.
Read next
This term is covered properly in Email courses: the complete guide to writing and finishing one, which is a longer piece on the subject.
Every other term is on the glossary index , the longer writing is in the guides, and what this site itself does is on the home page.
Thinking of writing one of these?
5dayemail hosts a five-to-ten day email course: you write it once, and everyone who joins your list gets one email a day, in order, starting from the day they confirm.
Accounts are opened a few at a time rather than by signing up. Leave your address and you will be written to when the next ones open.
One message, when there is room. No course emails, no newsletter, and the address is not passed on. Ask and it is deleted; what is kept, and for how long, is in the privacy policy.