The formulas
Open rate = Unique opens ÷ Delivered × 100
Click-through rate = Unique clicks ÷ Delivered × 100
Click-to-open rate = Unique clicks ÷ Unique opens × 100Example: 700 unique opens out of 2,000 delivered emails is a 35% open rate. If 70 people clicked, CTR is 3.5% and CTOR is 10% — one in ten people who opened went on to click.
Why open rates aren't what they used to be
Email platforms count an "open" when a tiny invisible image in your email loads. Since 2021, Apple Mail Privacy Protection can load that image automatically for people who turn the feature on — whether or not they actually read the email. Some other mail apps and security scanners also fetch images on their own.
The result: opens can be inflated (machine "opens") or missed (people who block images). So:
- Use open rate to spot trends on your own list, not to compare against other companies.
- Lean on clicks, replies and conversions for decisions — they require a real person.
- Be careful with automations that trigger on opens, like "send a follow-up to anyone who didn't open."
- Some platforms try to filter machine opens. Check your provider's documentation to see how it reports them.
Unique vs. total opens
Total opens count every open, so one enthusiastic subscriber can open five times. Use unique opens for open rate — that's why this calculator won't accept more opens than delivered emails.
Want more people to open in the first place? Check how your subject line looks on a phone with the Subject Line Preview, and track what happens after the click with the UTM Builder.