Click-to-open rate
Of the recipients who opened the email, the percentage who clicked a link.
Click-to-open rate (CTOR) is the percentage of email opens that resulted in at least one click, calculated as (unique clicks / unique opens) × 100. It isolates the quality of the email's body and CTA from the quality of the subject line. A subject line that gets opens but a body that doesn't convert shows up as high open rate / low CTOR.
CTOR is the metric to focus on when iterating on body copy, CTA placement, and email design. Subject-line A/B tests use open rate; body A/B tests use CTOR or downstream conversion. Healthy CTORs run 10–20% for lifecycle email and 8–12% for newsletters.
Apple Mail Privacy Protection's preemptive image loading has corrupted the "open" denominator, which means CTOR has become less reliable for Apple-heavy audiences (consumer DTC). For audiences skewing toward work emails (B2B, productivity SaaS), CTOR remains a clean metric. Always report CTR alongside CTOR — they tell different stories.