Click-to-Open Rate (CTOR) is an email engagement metric that measures the percentage of people who opened an email and then clicked a link inside it. Calculated as clicks divided by opens (not divided by sends), CTOR isolates email content quality from subject-line and deliverability performance.
CTOR = Unique Clicks ÷ Unique Opens × 100. An email opened by 4,000 people that produced 600 clicks has a CTOR of 15%.
The denominator is the key distinction. Click-Through Rate (CTR) divides clicks by total sends, mixing in subject-line performance and deliverability. CTOR divides by opens, isolating what happened after the customer chose to engage with the email.
CTOR earns its place because it tells you which half of an email program to fix, and the two halves cost very different amounts. If opens are healthy and CTOR is weak, the constraint is content and offer: the list is fine, and the fix is segmentation and creative, which is cheap and quick. If CTOR is strong but total clicks are low, the constraint is the size or the deliverability of the list, and the fix is list growth and sender reputation, which is slow and expensive.
Getting that diagnosis backwards is what costs money — months spent rewriting emails that were never the problem, while the addresses that would have bought quietly stopped receiving anything. Because open counts are inflated by mail privacy tools, read CTOR against your own history and between comparable segments rather than against another brand's number.
CTOR isolates email content performance. A subject line gets the customer to open; the content gets them to click. If CTOR is high but CTR is low, the subject lines aren't working — the people who do open like what they see. If CTR is high but CTOR is low, the subject lines are over-promising relative to the content.
Tracking CTOR alongside open rate and CTR is the cleanest way to diagnose where in the email funnel performance is lifting or lagging.
Highly variable by email type and audience:
Note that Apple Mail Privacy Protection and similar tools have inflated open rates since 2021, which depresses reported CTOR. The trend over time matters more than the absolute number.
Diagnosing a weak CTOR should determine which fix to reach for, not just confirm there's a problem: if CTOR is flat across an otherwise well-segmented program, the issue is usually template mechanics — a buried CTA, inconsistent hierarchy, or mobile rendering that a Klaviyo template design pass fixes directly — while a low CTOR on generic broadcast content with no segmentation points back to the flow and segment strategy under email and SMS marketing. Fixing the wrong one first is a common way teams spend a quarter redesigning templates that were never the bottleneck.
Reading CTOR in isolation from send volume, list growth, and deliverability trend gives an incomplete picture, so it’s worth pulling it into the same report as the other metrics that actually inform email decisions — a process covered in Klaviyo reporting and custom reports.
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