CTR is the share of recipients who click a link, a common but limited email engagement metric.
Key points
- CTR is a standard online marketing metric for ads, search results and emails [1][2].
- In Google Ads, CTR is clicks divided by impressions [3]; in email, Mailchimp divides unique clicks by delivered messages [4].
- Links in email are tracked by redirecting through the sender's domain, often a Custom Tracking Domain.
- Many cold emails contain no link, because the goal is a reply; then Reply Rate replaces CTR as the key metric.
- Security scanners may click links automatically, which inflates CTR in the same way privacy features distort Open Rate.
How CTR is calculated
The general definition is clicks divided by impressions: for a search ad, the number of clicks divided by how often the ad was shown. Google Ads documents this formula and uses CTR as one signal of ad relevance [3]. In email, the equivalent of an impression is a delivered message. Mailchimp calculates click rate as unique clicks divided by successfully delivered emails [4]. Click-to-open rate is a variant that divides clicks by opens, but it inherits the problems of open tracking. Optimizely describes CTR as a basic measure of how well a message or placement drives action [2]. Always compare CTR within the same channel and audience; benchmarks across industries vary widely.
Link tracking and its side effects
Email platforms track clicks by rewriting each link to point at a redirect URL on their own domain, which records the click before sending the reader on. Many senders use a Custom Tracking Domain so links match their brand. For marketing email this is standard. For cold outreach it has costs: rewritten links look less personal, shared tracking domains can carry a poor reputation and filters may weigh them. Automated link scanners in corporate mail systems also follow links to check them for threats, which records clicks no human made. For these reasons, some teams include at most one link in a cold email, or none, and focus on replies.
When CTR is the right metric
CTR fits emails whose goal is a visit: a newsletter, a content offer, a product update. It is less suitable for Cold Email, where the ideal outcome is a conversation, not a page view. If your outreach does include a link, such as a short case study, measure CTR alongside Reply Rate so you know whether the link supports the reply or replaces it. Use A/B Testing to compare link placement or wording, keeping everything else constant. And because both opens and clicks can be triggered by machines, trust metrics that require human effort, such as replies and a Meeting Booked, when deciding what works.
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