Learn the Right Way to Calculate Email Open Rate

On December 17, 2019
6min read
Denys Velykozhon Content Marketer @Mailtrap

In the blog post on Email Marketing Metrics, we broke down key performance indicators by their priority. Of more than 20 metrics, the open rate was highlighted as a pivotal one. It is a foundation slab on which you can build analytics of your email campaigns. On one hand, the email open rate is easy to calculate and work with. However, the metric has its own quirks that you should explore in detail.  We have collected essentials about the email open rate and introduced them below.

What is an email open rate for?

The open rate shows how many recipients of the entire mail list opened the email campaign. This metric defines the success or failure of the campaign. If the rate is good enough, you can go deeper and analyze other consequent metrics to optimize your emails. If the open rate is low, your key task is to increase it. 

Email open rate calculation formula

Formula #1

Open rate = (total unique opens ÷ total recipients) x 100

You need two variables to calculate the open rate:

  • Total recipients – how many email addresses are on your mailing list
  • Total unique opens – how many recipients opened your email 

Divide the number of opens by the number of total recipients and multiply the outcome by 100. 

Bear in mind that you need the unique opens only. If a recipient opened the same email twice or more, they only count as one unique open.

Formula #2

Open rate = (total unique opens ÷ (total recipients – bounced emails)) x 100

Some companies use a bit more refined formula for open rate calculation with three variables:

  • Total recipients – how many email addresses are on your mailing list
  • Total unique opens – how many recipients opened your email 
  • Bounced emails – how many emails failed to reach the inbox

For example, of 1K emails sent, 15 bounced, including soft and hard bounce. This means that 15 recipients did not open them due to a technical issue, rather than a poor engagement of the email campaign. This alternative formula provides more accuracy of open rate with a focus on the engagement.

How do you calculate email open rate for multiple campaigns?

Let’s say your last three email campaigns had the following open rates:

  • Campaign A: 16% 
  • Campaign B: 20%
  • Campaign C: 22% 

Add them all together and divide that by three:

(16 + 20 + 22) ÷ 3 = 19.3%

This is the average open rate for your email campaigns.

What is the difference between the open rate and the click-to-open rate?

The open rate mostly rests on the quality of subject lines and pre-inbox optimization. The click rate shows whether the email design panned out. The click-to-open rate (CTOR) blends the open rate and click rate into a single metric that measures the relevance and effectiveness of the email content. 

With the CTOR, you get an idea of how many recipients not only opened the email, but also clicked the CTA in it. Here is the formula to calculate the click-to-open rate:

Click-to-open rate = (total unique clicks ÷ total unique opens) x 100

For example, your email campaign was opened by 150 recipients, and only 42 of them clicked the CTA link. As a result, your click-to-open rate is 0.28 or 28%, which is good enough. According to different researches, the benchmark for the CTOR metric is 20-30%

Ways to track email opens

Email service providers mostly track email opens via tracking pixels and trackable links. There is also a read-receipt tracking mechanism that is rarely used nowadays. We explored each option in How Email Tracking Works. Here is a short summary. 

Tracking pixels

A tracking pixel is a piece of HTML code embedded in the email. Each tracking pixel is assigned an individual tracking number. When the recipient loads the email, the tracking number marks it as read. This is the most reliable way of tracking opens, which is used by many marketing platforms and email services, such as MailerLite or Amazon SES

However, this performance indicator is not 100% accurate. If the recipient’s email client has images and HTML turned off, the tracking pixel won’t load and report the open. Different marketing services use their own approaches to reduce this margin of error. For example, MailChimp factors in click-throughs with open rates.

Trackable links

A trackable link is a link generated with the use of tracking software and inserted into email content. So, trackable links are visible to the recipients, whereas tracking pixels are not. When the recipient clicks on this link, you get information about who opened the email and when. Trackable links are mostly created using UTM parameters, which allows you to track a wide range of user engagement data. Here is an example of a trackable link:


The problem here is that a recipient can open the email but ignore the link. In this case, the email won’t be marked as opened. 

Read receipts

It is also worth mentioning read receipts as a way to learn whether an email has been opened. They work as follows:

  • a sender’s email client sends a receipt request along with an email
  • once notified of the request, the recipient can either consent or decline to send a read receipt 

Truth be told, this tracking option is quite unreliable. If the recipient’s email client does not allow read receipts in the settings, you’ll never know whether the email has been opened. Besides, the read receipts mechanism mostly works if the sender and recipient use the same email client. 

Is my open rate good or not?

In addition to the quality of the email content and email list, the open rate depends on:

  • Email type – the open rate of transactional emails is usually two or three times more than marketing emails.
  • Industry – open rates in different industries can vary a lot. 
  • Sending date and time – to get the highest open rate, it’s crucial to identify the perfect day and time for launching an email campaign. 
  • Target region – open rates in different regions can vary a lot. 
  • Recipient’s device – open rates from mobile devices keep growing year by year.

All these factors matter. But what is a good email open rate on average? Take a look at the following benchmarks based on the many years’ experience of the Mailtrap marketing team: 

How to improve the email open rate?

The recipient ponders over two factors before deciding whether to open an email or not: subject line and sender name. So, if you need to raise the open rate, make sure to optimize both of them.

Use a proper sender name

People prefer to interact with people. That’s why an email sent from a specific contact person has more credibility with recipients. So, instead of using a general email address, such as “Marketing crew” or “Support team”, opt for something like “Jane from [Company name]”.

General email addresses reduce the open rate, while personal email addresses can lift it by 15+%.

Another valuable tip for increasing the credibility of an email sender is to use the Brand Indicator for Message Identification or BIMI. This is a DNS TXT record that allows brands to display their logo next to each email in the inbox. Here is how emails from different brands may look in an inbox before and after the BIMI implementation:

For more on how to join the BIMI club, read our blog post Do Your Emails Need BIMI?

Fine tune the subject line

The subject line of your email campaign must be:

  • Concise – subject lines with up to 10 words have the best open rates. Keep in mind that your recipients open emails from mobile as well. That’s why the optimum length of the subject line is up to 90 characters.
  • Relevant – if a recipient ignored your previous emails about discount offers, he or she is unlikely to open them this time. In this case, it’s better to segment your email list. This will let you increase the subscribers’ engagement. 
  • Apprehensible – let recipients understand right in the subject line what you want them to read. 
  • Catchy – when a recipient scans his or her inbox, your email has a few seconds (three or four) to catch the eye. So, the open rate of your email campaign depends on whether the subject line manages or fails to draw the recipient’s attention. 
  • Personalized – personalized subject lines – those containing a recipient’s name – usually show better open rates. However, adding “Hey [subscriber’s name]” to the subject line are unlikely to raise your rates significantly. Be creative and you’ll be able to take the biscuit.

Besides the aforementioned best practices, you should also avoid the following in your subject lines:

  • Spam trigger words such as No costOne-of-a-kind dealRisk-free, and many many more.
  • Words typed with Caps Lock jammed
  • !!!!!!!!! or $$$$$$

How to get a smile on your face after the open rate calculation?

Always test your email campaigns before sending them! 

Each email goes through authentication mechanisms and spam filters implemented on SMTP and IMAP (or POP3) servers. So, you need to test:

  • the email sending capability of your appsend a test email for this. The best way is to use a dummy SMTP server like the one offered by Mailtrap. It provides an email sending sandbox to test your emails without actually sending them. For more on the available features and functions, read the Mailtrap Getting Started Guide.
  • the SMTP relay – whether your SMTP server can route emails to the proper destination SMTP server. You can use Telnet or one of the web-based tools such as MX toolbox. Check out our blog post on Test SMTP Relay for details.
  • the email for spam – run tests for deliverability, spam, and email address validity. There are a bunch of online tools for thus, which we introduced in the Email Testing Checklist.
  • the email content – preview your email, test its HTML and body copy, as well as the subject line. This is a final flourish, after which you can click the Send button.

Once all the tests have been passed successfully, track your email marketing metrics and enjoy the results. The smile on your face is guaranteed!

Article by Denys Velykozhon Content Marketer @Mailtrap


1 replies


We’re delivering content on a weekly basis. We send two emails – one on Thursday to our entire email list and another one on Sunday to everyone who didn’t open the first one.

What you suggest in the “How do you calculate email open rate for multiple campaigns?” section is to calculate an average but that’s quite discouraging as the second campaign’s open rate is much lower than the first one (totally expected as this is a backup strategy) which will artificially decrease our overall open rate.

Looking into the data, our second campaign registers lower open rates. For the sake of keeping our open rates higher, one would think about getting rid of this second email. However, from a customer perspective, we still generate more opens and more clicks just because of this second campaign which is GOOD for the business. That made me think about whether the approach you suggest is relevant and I’d love to hear your perspective on that matter.

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