Email Open Rate & CTOR Calculator

Understanding the email open rate and CTOR calculator — concept and principle

Email marketers judge campaigns with three linked ratios: the open rate (how many recipients opened), the click-through rate or CTR (how many recipients clicked) and the click-to-open rate or CTOR (how many of those who opened went on to click). This calculator gives all three from delivered, opened and clicked counts, so you can compare subject lines, content and audiences.

How it is calculated

• Open rate (%) = unique opens ÷ emails delivered × 100
• CTR (%) = unique clicks ÷ emails delivered × 100
• CTOR (%) = unique clicks ÷ unique opens × 100

Use delivered emails (sent minus bounces), not sent emails, and use unique counts so one person opening five times counts once.

The principle

The three ratios split the email funnel into stages. The open rate mostly reflects the sender name, subject line, timing and list quality, because those are what people see before opening. CTOR isolates the content: among people who actually opened, how convincing were the message and call to action? CTR combines both, since CTR = open rate × CTOR. Separating them tells you where to work: a low open rate points to the subject line or deliverability, while a low CTOR points to the content.

Worked example

1. Inputs: 10,000 delivered, 3,100 unique opens, 420 unique clicks.
2. Open rate: 3,100 ÷ 10,000 × 100 = 31%.
3. CTR: 420 ÷ 10,000 × 100 = 4.2%.
4. CTOR: 420 ÷ 3,100 × 100 = 13.55%.

Check: 31% × 13.55% ≈ 4.2%.

How to read the result

Benchmarks differ by industry, list type and email provider, so your own history is the most reliable comparison. Open rates became less reliable after Apple Mail Privacy Protection was introduced in 2021: it can load tracking pixels automatically, recording opens that never happened. For that reason many teams now treat clicks, CTR and conversions as the main measures and use opens mainly to compare subject lines within the same list.

Common mistakes

• Dividing by emails sent instead of emails delivered.
• Using total opens or clicks instead of unique counts.
• Comparing CTOR from one campaign with CTR from another.
• Calling a campaign successful on opens alone when few people clicked or bought.

Frequently asked questions

What is the difference between CTR and CTOR?

CTR divides clicks by all delivered emails; CTOR divides clicks only by those who opened.

Why is my open rate suddenly much higher?

Automatic image loading by privacy features or security tools can inflate opens.

How can I raise CTOR?

Use one clear call to action, put it near the top and make the link text specific.

Sources: Apple, About Mail Privacy Protection (Apple Support)