2015 Subject Line Test Results: You might be surprised!

Vivian Swertinski

What makes a subject line engaging to you? Do you respond to personalization? Do you like subject lines that are fun and playful? Oftentimes marketers choose what would work for them and run with it. But do you know what really works best for your audience? Savvy marketers know that subject line testing is the only way to stay in front of audience engagement. In our pursuit to find out what audiences most respond to, we analyzed over 5,000 subject line test results for our webinar, The Best Subject Lines of 2015. What we found may surprise you!

Check out the recorded webinar here or view the slides here. Here are a few of the key findings by category.


In head to head tests, personalized emails consistently outperform non-personalized communications. The use of a recipient’s first name was the most prevalent amongst the test data, but we were encouraged to see several examples of profile and geographic data used as well. The subject line, “Your membership has an expiration date of ‘Expire Date’” is a good example of using data to customize subject lines by recipient. This particular subject line generated an open rate of 52%, which is far above the benchmark average of 35%. Other personalized fields that performed well were company name, chapter name, and geographic data such as city and state.

Use of “Free”

Outside of the song “Free Bird,” is there a phrase with “free” in it that you wouldn’t be inclined to at least look into? (Ok, “Free Bird” too, who am I kidding.) Audiences seem no different in 2015 as subject lines that included the word “free” performed quite well. It is our observation that the word free works in many — but not all — situations. For example, “Register Today – Free Breakfast on Saturday” (58% open rate) performed well above the 2015 benchmark. We observed that people respond well to invitations for free food. The following subject line sums our observation up nicely: “Did someone say free food?” (68% open rate). When appropriate, you may want to consider testing the word free or a similar term in your 2016 subject line testing. Which brings us to…

Play on Words

A big theme with subject line tests were playing with the words used, be it the order of words or using a synonym as a substitute to test against. An interesting example of this is using the word “complimentary” instead of “free.” The word complimentary gives a message of being special and may be more appealing based on what you are giving the recipient. Complimentary services seem to outperform “free” services. For example, “Complimentary Online CME Courses” (29% open rate) performed better than “Free Online CME Courses” (26% open rate).

In the 2015 Informz Benchmark Report, we noted that subject line testing was on the rise and we anticipate the momentum to continue throughout 2016. Savvy marketers know that testing is an essential component in their strategic marketing plan. Continue to evaluate your email marketing plans and make subject line testing a part of your 2016!

To download the 2015 Benchmark report, click here.


About the Author
Vivian Swertinski

As the Strategic Services Manager at Informz, Vivian partners with clients to maximize their digital marketing efforts with customized strategies leveraging the Informz marketing automation platform. Outside of work Vivian enjoys shopping, boating and volunteering her time to help disabled individuals in the community.