When should I use CTOR instead of CTR?
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The short answer: use CTOR when you're evaluating your content, and use CTR when you're evaluating overall campaign performance.
Here's the practical difference. CTR measures engagement across your whole delivered list. CTOR measures engagement only among the people who opened. That means CTOR removes the subject line from the equation. If you're testing two versions of your email body, CTOR isolates whether the content worked. Two campaigns can have the same CTR but very different CTORs, which tells you that one had a stronger subject line rather than better content.
Use CTOR when you're:
- A/B testing email copy or call-to-action placement
- Diagnosing why a campaign underperformed despite strong opens
- Comparing content performance across different audience segments
Use CTR when you're:
- Reporting on full campaign performance to stakeholders
- Comparing campaigns where open rates are similar
- Looking at how your whole list responds, not just the openers
One caveat: CTOR relies on open data, which has been unreliable since Apple Mail Privacy Protection started inflating open counts in 2021. If machine-opens are skewing your denominator, your CTOR will look lower than reality. Keep that in mind when comparing across time.
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