Open rate is the percentage of delivered emails that were recorded as opened. It is calculated by dividing the number of unique opens by the number of emails delivered, then multiplying by 100.
That is the whole definition. The tricky part is knowing what the number actually tells you, and what it doesn't.
How opens get counted
Most email tools track opens with a tiny invisible image placed in the email. When the recipient's email app loads that image, the tool records an open.
This method has gaps you should know about:
- Images blocked: some people and some company mail systems don't load images, so a real read is never counted.
- Automatic loading: some email apps and privacy features load images on their own, so an open can be recorded when nobody read anything.
- Security scanners: some business mail filters open links and images to check them, which can create opens that aren't human.
So treat open rate as a rough signal, not a precise count.
Why it matters when you're doing outreach
Even with those gaps, open rate is useful for a few practical jobs.
Spotting delivery problems. If a campaign that normally gets steady opens suddenly drops close to nothing, your emails may be landing in spam. That's a cue to check your sending setup, such as SPF, DKIM and DMARC, and whether your sending domain needs a rest.
Comparing subject lines. The subject line and sender name are most of what someone sees before deciding to open. Testing two subject lines on similar lists gives you a rough comparison. A list of cold email subject line ideas is a good place to start.
Deciding who gets which follow-up. Opened and not-opened are different situations. Someone who never opened probably never saw your pitch, so a fresh angle or a new subject line makes sense. Someone who opened but didn't reply saw it and needs a different nudge.
A concrete example
Say you run a small web design studio and email 200 local restaurants you found on Google Maps.
- 200 emails sent
- 10 bounce, so 190 are delivered
- 76 unique recipients are recorded as opening
Your open rate is 76 ÷ 190 × 100 = 40%.
Now look further. Of those 76 openers, 4 replied, and 1 booked a call. The open rate looks healthy, but the email body or offer is what decides the replies. If you only watched opens, you might think the campaign worked well, when the real question is why 72 people read it and said nothing.
You could then split your next step:
- The 114 who didn't open get a short follow-up with a new subject line.
- The 72 who opened but didn't reply get a follow-up that adds one specific detail, such as a quick note about their site's mobile menu.
That split is the core of a sensible follow-up sequence. The not-opened follow-up strategy post goes deeper on the first group.
Common mistakes
Treating opens as interest. An open means an image loaded. It doesn't mean the person read, liked or remembered your email. Replies and booked calls are the numbers that pay you.
Comparing your number to someone else's. Open rates vary with the audience, the list quality, the tracking method and the email apps your recipients use. Compare your campaigns against your own past campaigns instead.
Chasing opens with clickbait. A misleading subject line can raise opens and lower trust in the same move. Write a subject that honestly matches the email.
Ignoring list quality. Sending to old or guessed addresses causes bounces and can hurt your sending reputation, which then drags down opens on every campaign. Build a clean lead list and verify it before sending.
Testing on tiny samples. If you send 20 emails per version, a couple of random opens can swing the result. As a rule of thumb, wait until each version has gone to a decent number of people before deciding a winner, and treat small differences as noise.
Reading opens as counts. Many tools show whether someone opened, not reliably how many times. Even where a count exists, repeated opens can come from forwarding or scanners. Use opened or not opened, and leave it there.
What to do next
Use open rate as a health check and a routing signal, then put your attention on replies.
- Track it per campaign so you notice sudden drops.
- Fix delivery first if opens fall sharply. Consider whether you should use a secondary domain for outreach to protect your main one.
- Test one thing at a time, usually the subject line, and keep the rest of the email the same.
- Branch follow-ups on opened versus not opened, rather than sending everyone the same second email.
- Judge the campaign on replies and meetings, not opens.
In GetClient, campaign analytics show opens per campaign, and the flow builder can branch a follow-up on If Opened or If NOT Opened, with delays in days, hours or minutes. The branch is yes or no only, which fits how unreliable open counts are anyway. You can also verify a list before sending to cut bounces. New accounts get 100 free credits without a card; see plans and credits for details.