Boris Grinkot

Reader Mail: Understanding differences in clickthrough rates and open rates

August 12th, 2011

Recently, my colleague Brad Bortone forwarded me an inquiry from one of our readers, who asked the following:

Can you provide any insight into why my newsletter emails would receive a 10% unique CTR and a 3% open rate? Aren’t open rates generally the larger number?

We use XXXXXXXX as our email service provider. Could this be related to how our newsletter renders in the preview pane of email clients?

In thinking about this, I realized that many email marketers may be asking the same questions, and could benefit from an extensive reply. Besides, I don’t get much mail around here, so I was excited to help out.

Here is what I wrote in my initial reply:

Like most people, I rarely open messages in my email client, but rather just read them in the preview pane. And, also like most people, I do not have images automatically load in my email client.

If an email is not especially dependent on graphics (in that it doesn’t look “broken” without them), then a user is even less likely to turn on images in the email client, which means that the tracking pixel never registers the open.

As such, this significantly depresses the reported open rate, which can cause the observed difference. In addition, if the CTR is measured as visits divided by opens, then you have an underestimated number in the denominator, and a probably pretty valid number in the numerator (since “clicks” are measured on the page as “visits”) — meaning that the result (CTR) is inflated.

(For those who may not know, a tracking pixel is a method for tracking user actions in which an 1×1 px image is placed on a Web page or HTML-based email to track user behavior and activity.)

Here is a more detailed, numerical example to illustrate how clickthrough and open rates can vary. Let’s start with the following scenario:

Emails delivered = 1,000
Emails opened (based on tracking pixel) = 100
Unique clickthroughs from email to landing page (based on visits to landing page or redirect URL tracking) = 50

Open Rate = 100 / 1,000 = 10%
Clickthrough Rate = 50 / 100 = 50%

It’s important to understand that while CTR is calculated correctly, the 50 unique clicks may not be from the same 100 people who opened the email. The problem is that “open” tracking technology relies on a recipient’s email client setup, which typically does not load images by default.

The email protocol does not send back an implicit “open” receipt to the sender, so we have to rely on tracking pixels to signal an “open.” If images are not loaded, the tracking pixel is rendered useless.

In contrast, the count of clickthroughs based on unique visits or redirect URLs with unique parameters for each email recipients is much more reliable. In reality, the following may be happening:

Emails delivered = 1,000
Emails opened (actual, but effectively unknown to the marketer) = 250
Unique clickthroughs from email to landing page (based on visits to landing page or redirect URL tracking) = 50

Open Rate = 250 / 1,000 = 25%
Clickthrough Rate = 50 / 250 = 20%

So the figures that we see show open rate and clickthrough rate as 10% and 50%, respectively, while in reality (which our tools can’t show) the open rate and clickthrough rates are 25% and 20%, respectively. However, this doesn’t mean you should throw in the towel. The data you do get is still very valuable, and it can be used to track optimization efforts.

Here are a few thoughts on how to use it:

First and foremost, I would not compare the two numbers to one another, as they measure significantly different things. Consider these two opposite scenarios:

  1. You may have a very effective subject line that gets recipients to open the email, but once they read the content, they realize it’s not applicable to their needs and never click. Open rate would exceed clickthrough rate.
  2. Conversely, if the subject line can only be deciphered by recipients who are already highly interested and familiar with the offer, then few people will open the message. But, most of those who do, will click through. Clickthrough rate would then exceed open rate.

These numbers are great to use when comparing multiple campaigns that are sent to the same list. Testing different subject lines is the only way to understand how you can increase the open rate for one particular list. You should also test subject/content combinations if your sample size is large enough, to introduce more variables.

Likewise, testing the same subject line on different lists can tell you what works best for each segment, or which list is of higher quality. Testing email content will give you different clickthrough rates to compare and improve … and possibly indicate whether or not you should buy more or less from the same list provider.

Related Resources

Members Library — Email Marketing: How a triggered alert program maintains 40% open rate, 60% click-to-open rate for millions of subscribers

Members Library — Marketing Research Chart: Email deliverability metrics improving … slightly

Email Marketing: Three lessons learned at the MarketingSherpa Email Marketing LEAPS Advanced Practices Workshop

MarketingSherpa 2011 Email Marketing Benchmark Report

Boris Grinkot

About Boris Grinkot

Boris is part social scientist, part techie, and part philosopher. As the director of technology consulting at a small Florida marketing firm, he began searching for ways to combine web development with his academic background in research. This search led him to MarketingExperiments at MECLABS. Since joining the team in 2007, Boris’ work with Fortune 500 and international research partners has included experimental design, business intelligence analysis, competitive strategy, and lead generation. He has led optimization projects that generated up to tens of millions of dollars in annual revenue. Boris holds an MBA from the University of Florida and a B.A. in Religious Studies with a cert. in International Relations from Cornell.

Categories: Email Marketing Tags: , , , ,

  1. August 15th, 2011 at 03:46 | #1

    Hi Bob,

    Thanks for sharing this – we have just embarked on some email marketing and this helps explain our stats.


  2. August 15th, 2011 at 04:28 | #2

    Great article Boris on a really important topic – that of understanding and using your KPIs to improve your email performance.

    Two things though:
    – If the email tool is only using the tracking pixel to determine the open rate you are potentially in bad shape. It should keep track of link clicks, forwards, shares etc and include those when calculate open rates to better represent the email performance. In my view it should not be possible for the Open rate to be exceeded by the CTR. If someone clicks, they must have read it (proxy for open).
    I totally agree that many people do not download images (mobile devices, previews etc) and hence only relying on the tracking pixel is really not best practice.

    – Did you not mix up your conclusion in point 1 and 2? If a lot of people open but few click, the open rate would exceed the CTR and conversely, if few people open it but almost everyone who do, click, the CTR would exceed the Open rate (again – the CTR should not be allowed to exceed the open rate IMO).

    For a tool that does get Open and Click rates right, check out

    CMO |

  3. Boris Grinkot
    Boris Grinkot
    August 15th, 2011 at 10:37 | #3

    @Klaus Trolle
    Thank you for catching my mistake Klaus — I was getting too excited and careless toward the end of the post. It’s fixed now.

    On your first point, I agree that counting all clicks as proxies for opens gets you closer to the true number of opens. However, there’s always a blind spot: recipients who opened the email without the pixel firing AND did not click or forward, etc., still would not be counted, meaning that the reported open rate would under-represent the reality. Still, what I said about the usefulness of this metric doesn’t change.

    Also, I would maintain that CTR can indeed be greater (or smaller) than Open Rate. The two metrics are independent. If you are measuring CTR with the number of emails delivered in the denominator, then you would be right — but that’s not the typical formula for CTR (not the one I used above, anyway), though a good way to measure email effectiveness, especially given the problems around tracking opens.

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