Call to action (CTA)

In short: A call to action, CTA for short, is the explicit invitation to take the one step that an email is meant to trigger – usually a highlighted button or link such as “Reserve a place” or “Read the full article”. In a newsletter, the CTA is the point where reading turns into a click.

What makes a CTA in emails

The term comes from general marketing, where it means any call to act, including on posters or on the radio. In an email it takes a measurable form: it is a link. Every click on it can be counted, which makes it possible to check whether the mailing achieved its goal.

Three questions help with the wording:

What exactly happens after the click? A link text such as “Sign up for the workshop on 14 March” says so; “Click here” does not.
What is the main goal? Several equally strong calls compete with one another. One main CTA and a few quieter secondary links are easier to evaluate.
Where does it go? Readers who learn the purpose of the email in the first paragraph do not have to search for the CTA at the end. In long newsletters the same link can be repeated further down.

Accessibility: what WCAG 2.2 says

The W3C’s Web Content Accessibility Guidelines 2.2 apply to web content, but can be transferred to HTML emails. Three success criteria concern the CTA directly:

Link Purpose (2.4.4, level A): The purpose of each link must be recognisable from the link text alone or together with its context.
Contrast (1.4.3, level AA): Text needs a contrast ratio of at least 4.5:1, large text at least 3:1. This also applies to the lettering on a coloured button.
Target Size (2.5.8, level AA): Click targets should be at least 24 × 24 CSS pixels or have enough spacing from other targets.

A button that consists only of an image is invisible when images are not loaded. A button made of HTML and text with a background colour, by contrast, stays readable. The text version of the email (the text/plain part in multipart/alternative, RFC 2046) needs the link as a written-out address.

How it differs

CTA and link: Every CTA is a link, but not every link is a CTA. The unsubscribe link, legal notice (Impressum) or web version are fixed components or service links.
CTA and conversion: The click on the CTA is an intermediate step. The conversion rate measures whether what the email was about then happens on the website.

Easily confused

Clicks are not always people. Security features such as Safe Links in Microsoft Defender for Office 365 check addresses in emails before delivery and open some of them in the background. Automatic retrievals of this kind, called bot clicks, can increase the click rate of a CTA.
Five times “Learn more”: If a newsletter contains several links with the same text, they cannot be told apart in a screen reader’s list of links. WCAG 2.2 requires the purpose to be clear from the link text or its context.

Example

A club newsletter invites people to its summer party. Weak would be: “More info – click here”. Better:

<a href="https://example.de/sommerfest/anmeldung"
   style="display:inline-block;padding:12px 20px;background:#0b5d3b;color:#ffffff;">
  Sign up for the summer party on 21 June
</a>

The link text says what happens; white on the dark green achieves well over 4.5:1, and with the padding the area is larger than 24 × 24 pixels. In the text part, the same call appears with the address written out.

Frequently asked questions

What is a call to action in simple terms? The invitation to do something specific now – in a newsletter almost always a click on a link or button.

How many CTAs belong in a newsletter? There is no fixed number. A clear main goal makes evaluation easier; a newsletter with several topics often has one link per item.

How do I measure whether a CTA works? By the clicks on exactly this link in relation to the emails delivered, or better still by what then happens on the website. Anyone comparing two versions checks the difference with a significance test.

Matching tool

Metrics calculator: click rate and click-to-open rate from your figures.