When I started in digital marketing in 2014, I immediately started researching metrics to measure the results of my efforts.
The email opening rate was an indicator that I had immediate contact with, however it was far from having all the information to be able to “manipulate” it.
If you are interested in knowing everything there is to know about this indicator, including how to optimize it, stay with me!
How to correctly calculate the open rate of an email
The calculation of the opening rate of an email is carried out using a very simple equation.
$$\text{OR} = { \text{umo} \over \text{sm} – \text{rm} } \times 100$$
To understand the equation in its entirety, let’s look at the meanings of the abbreviations.
$$\text{OR} = { \text{Open Rate} }$$
$$\text{umo} = { \text{Number of Unique Messages Open} }$$
$$\text{sm} = { \text{Number of Sent Messages} }$$
$$\text{rm} = { \text{Number of Returned Messages} }$$
We will not just focus on the definition of the formula. Let’s do a practical example here to avoid any doubts regarding the calculation.
Let’s imagine that our email marketing campaign was sent to a set of lists that had a total of 675 contacts. As we did not clean the list, 14 emails were returned and after observing email openings during the five days following sending the email communication, we totaled 245 unique openings.
Passing these numbers into our mathematical formula, we have:
$$\text{OR} = { 245 \over 675 – 14 } \times 100$$
$$\text{OR} = { 245 \over 661 } \times 100$$
$$\text{OR} = 37,06\% $$
In the next point we will discuss what constitutes an acceptable opening rate within current market parameters so that we can interpret the result obtained of 37.06%.
How to know if your email open rate is acceptable or not
There are some controlled experiments carried out around the topic of open rates in email marketing and conclusions based on aggregated data lead us to open rates between 25% and 36%, although the averages for the various industries are fixed at 18%.
From what I have experienced, as a result of observations in my email marketing activity, I consider an open rate above 25% to be minimally acceptable. Open rates of just 25%, at least to me, are a sign that I have some work to do in regards to list cleanup.
So, at least for me… minimally acceptable, 25%, acceptable 30% and above.
Factors that influence the opening rate of an email
There are three very relevant factors that have a direct influence on the opening rate of an email.
- Email subject line/title
- Quality of email list segmentation
- Time and day of the week the email was sent
I will detail the relevance of each of them.
Email subject line/title
The email title, also known as the email subject line is extremely important for a good open rate.
In a study by University College Roosevelt in 2019, three subject lines were compared. One personal, one emotional and one short.
The personal line: [name], have you organized yourself for a new year of saving?
The emotional line: Save this new year. Limited Stock.
The short line: New Year’s Eve with affordable prices.
The results were shown in the table below.
| Test | Number of Characters | Open Rate % |
| Personal | 47 | 25 |
| Emotional | 37 | 26.1 |
| Short | 31 | 26.9 |
I personally have mostly used emotional and personal subject lines. I rarely manage to fit a short title.
Quality of email list segmentation
Good segmentation of the contact list will influence the opening rate. However, the important thing in segmentation is not just optimizing for opening, but rather reconciling the opening objective with the desired result. We’re not just here to be the champion of open rates, we also want results.
For this segmentation work to be done well, it is first necessary to determine the segmentation criteria. These criteria can, for example, be based on global presence strategies or increased sales.
For example, in the case of global businesses it is always a good practice to segment by location. Different countries have different cultures, so geographic segmentation may in most cases make sense. We optimize not only for the opening rate but also for the result of communicating according to the culture of the country in question.
If the objective is to increase sales, it might be a good idea to create a segment with customers who have already made several purchases. Again, we are optimizing for the opening rate as this customer is familiar with the brand and will most likely open the email and at the same time we are optimizing for the result, as it is very likely that a customer who has already made repeat purchases will repeat again.
Time and day of the week the email was sent
When it comes to this question, there is no direct answer. There are, however, several studies that indicate the best time intervals and the best days of the week.
The author Matija Žiberna in his master’s thesis dated 2020 on “Email Marketing in Starups – An empirical analysis on the effect of reciprocity” where among a series of other issues he also touches on the subject of hours and days of the week and their relationship with the open rate.
The data tells us that the best days to optimize for open rate are weekends (Saturday and Sunday) and that the best days to optimize open rate are Monday, Tuesday and Wednesday.
When it comes to hours for optimizing opening rates, the best time to send is between 10am and 11am, as most openings occur between 9am and 3pm.
I personally ship on Mondays and Tuesdays and shipping times tend to be around 7am.
A/B testing to improve email open rates
A/B tests, also known as split testing, are essentially comparative tests of two versions of content where we test version A against version B and measure the results.
These tests can be carried out continuously and will mainly give us clues for optimization and recommend changes.
In email marketing, A/B tests must be carried out on the subject lines, the images used and the calls to action (CTA), in Portuguese “appeals to action” or “calls to action”. In turn, the segments must be tested using the same methodology. Segment A against segment B in order to determine which combinations generate higher opening rates.
Conclusion
We learned that the email opening rate in the context of email marketing goes a little further than its simple calculation and that there are a series of factors that are important to understand due to the simple fact that they have a direct influence on this metric.
It is therefore important to remember that to influence the opening rate of an email we will have to focus on 3 factors. Email subject line/title, quality of email list segmentation, and time and day of the week the email was sent.
In order for the combinations of these three factors to work optimally, we will have to use A/B tests in order to arrive at the combinations that generate the highest number of open rates.