Open rate is opens divided by delivered emails, not by emails sent. The distinction matters because bounces never reached anyone, so leaving them in the denominator penalises you twice for a bad address. Delivered is sent minus bounced, and every serious email platform reports open rate on that basis, which is why a hand calculation using the sent figure will always come out lower than the dashboard.
Open tracking works by loading a tiny invisible image, so it has always been an approximation. Text-only clients and blocked images produce opens that are never recorded, while privacy features that pre-fetch images record opens that never happened. The practical consequence is that open rate is now unreliable as an absolute measure and should be used only for comparison between similar sends, with clicks treated as the real signal of interest.
Click-to-open rate is the more useful derived figure, because it asks what share of the people who opened went on to click. It separates the subject line, which drives opens, from the content, which drives clicks. On the sample entries 5,310 opens from 23,580 delivered is a 22.52% open rate, 742 clicks give a 3.15% click rate, and the click-to-open rate is 13.97%.
The formula
Sent- Emails despatched
Bounced- Emails that never reached an inbox
Delivered- Sent minus bounced — the correct denominator
CTOR- Clicks ÷ opens × 100, the click-to-open rate
How to use this calculator
- Enter the number of emails sent and how many bounced.
- Enter unique opens and unique clicks recorded.
- Add unsubscribes to see the list attrition from this send.
- The gauge shows open rate on delivered mail; click and click-to-open rates follow.
Worked examples
24,000 sent with 420 bounces
Delivered is 23,580, so the open rate is 5,310 ÷ 23,580 = 22.52%. Using the sent figure instead would report 22.12%, understating it by 0.39 points purely by counting mail that was never received.
Separating subject line from content
742 clicks on 23,580 delivered is a 3.15% click rate, but 13.97% of the people who opened. If the next send lifts opens to 30% without moving click-to-open, clicks would rise to about 988 — the subject line did the work, not the content.
How to read your score
Frequently asked questions
Should open rate use sent or delivered?
Delivered, which is sent minus bounces. A bounced email could never be opened, so including it in the denominator confuses list hygiene with content performance.
Why is open tracking unreliable now?
It depends on loading a tracking image. Privacy features that pre-fetch images register opens nobody made, while blocked images hide genuine ones. Use it for relative comparison between sends, and rely on clicks for anything that matters.
What is click-to-open rate for?
It isolates content from subject line. Open rate tells you whether the subject earned attention; click-to-open tells you whether the message deserved it. A high open rate with a poor click-to-open usually means the subject line overpromised.
What bounce rate is acceptable?
Under 2% for an established list. Above that, mailbox providers begin to treat the sender as careless, and deliverability falls for everyone on the list. Hard bounces should be removed immediately.
Email metric reference
| Metric | Numerator | Denominator | Value |
|---|---|---|---|
| Open rate (delivered) | 5,310 opens | 23,580 delivered | 22.52% |
| Open rate (sent) | 5,310 opens | 24,000 sent | 22.12% |
| Click rate (delivered) | 742 clicks | 23,580 delivered | 3.15% |
| Click-to-open rate | 742 clicks | 5,310 opens | 13.97% |
| Bounce rate | 420 bounces | 24,000 sent | 1.75% |
| Unsubscribe rate | 96 unsubscribes | 23,580 delivered | 0.407% |
Six figures from one send. Always state the denominator when quoting any of them.
| Delivered emails | CTOR 5% | CTOR 10% | CTOR 14% | CTOR 20% | CTOR 30% |
|---|---|---|---|---|---|
| 2000 delivered | 23 clicks | 45 clicks | 63 clicks | 90 clicks | 135 clicks |
| 8000 delivered | 90 clicks | 180 clicks | 252 clicks | 360 clicks | 540 clicks |
| 23580 delivered | 266 clicks | 531 clicks | 743 clicks | 1,062 clicks | 1,593 clicks |
| 60000 delivered | 676 clicks | 1,351 clicks | 1,892 clicks | 2,702 clicks | 4,053 clicks |
| 200000 delivered | 2,252 clicks | 4,504 clicks | 6,305 clicks | 9,008 clicks | 13,511 clicks |
Holding the open rate at 22.52%, so only the content performance varies.