A/B Testing for Subject Lines: 10 Tips, Tricks, and Twists

Pick your favorite. Which of the following titles gets you most excited about reading the rest of this article?

• Ten Considerations for Split Testing Newsletter Subject Lines

• What Is A/B Testing in Email? How To Improve Your Subject Lines

• A/B Testing for Subject Lines: 10 Tips, Tricks, and Twists

• The Open Sesame of Open Rates: Subject Line A/B Testing

Sadly for me, I don't get to ask my readers this question before publication. You do.

Most publishers and content creators rank open rate as the most important metric for their email newsletter. Testing your subject line with a small subset of your audience helps ensure that the best subject line is sent to your subscribers.

Here's how to do it and tips to help you do it well.

What Is Subject Line A/B Testing?

Subject line A/B testing is the process of sending out two (or more) different versions of an email with different subject lines to see which one performs better. It's an important part of data-driven email marketing and publication.

You can apply A/B testing (also called split testing) to almost any aspect of your content, but your subject lines are most likely to have the highest impact on the open rate.

After all, most email recipients (32.72%) say that subject lines are the most important factor in persuading them to open an email. Subject lines even squeak past the sender's name or company (32.37%).

The impact of testing is significant. For example, beehiiv creator Alex Banks of Through the Noise regularly uses A/B testing for a 5-6% bump in his open rates.

How Should I Set Up My A/B Test?

Note: This article is all about how to create effective A/B tests. For the nuts and bolts of setting one up for your beehiiv newsletter, check out this tutorial on creating subject line A/B tests.

For the test results to be meaningful, they need to be statistically significant. In other words, the outcome can be attributed to the changing variable (the subject line) rather than simple chance.

3 Tips For Effective A/B Tests

Generate statistically significant results by setting the proper parameters for your test.

Use a Sample Size of 10-20% of Your Audience

The exact number will depend on your total audience size. You need to send each version to enough people that the data provides a meaningful outcome while minimizing the number of subscribers who receive a non-winning subject line.

The sweet spot typically rests in the range of 10-20% of your audience.

Remember, the more data you gather, the more reliable the test. You can still profit from A/B testing as a smaller publication but put a mental asterisk next to your results. Avoid over-extrapolating to large conclusions about your audience.

Test 2-4 Subject Lines

A standard A/B test has two versions of a subject line (version A and version B), but you can test more variations.

However, we don't recommend testing more than four subject lines. The number of subject lines you test impacts sample size. Fewer variables allow you to use a smaller total test audience.

In addition, you want to be able to learn from your tests and apply those lessons going forward. The more versions you have, the more subtle differences that pile up, and the harder it is to extract a clear takeaway.

Run Your Test for 2-3 Hours

It's critical to run your test long enough to gather enough data. Based on our historical performance analysis, 2-3 hours provides the necessary time to collect enough data.

Once the test is complete, the winning subject line is automatically sent to the remaining subscribers.

Remember that if you usually send a newsletter at a specific time, your subscribers develop expectations. That's around when you should send your winning email to the majority. A significant departure can impact your open rate negatively.

How Should I Use A/B Subject-Line Tests for Long-Term Growth?

One of the beautiful things about A/B testing through beehiiv is that short-term, data-based decision-making is automatic. After setting it up, you can sit back while the robots gather and respond to the data.

The ideal A/B test also teaches you something about your audience, providing you with information you can use to sharpen your subject-line skills and helping you develop a loyal readership.

3 Tricks for Incorporating A/B Tests Into Your Process

Keep these best practices in mind to pair immediate subject-line improvements with long-term success.

Develop a Clear Hypothesis or Question

Your growth as a creator requires you to understand the why of your results. Then, you can use A/B email testing to improve long-term engagement.

Just like in science class, you can start your A/B test with a hypothesis. What do you believe will increase your open rates? Formulate your theory and test it out.

Another approach is to identify a clear point of difference between the two subject lines. Will your audience respond better to a question or a statement? Do they want to learn something or be entertained?

Again, don't over-extrapolate, but see if you can identify patterns across issues.

Never Lose Sight of the Big Picture

Information junkies, I'm talking to you. Don't sacrifice either your vision or your audience's experience in your data-based, growth-hacking quest.

Don't let A/B testing overwhelm your creative process.

If you're only using new subject lines to boost your open rates without considering the impact on other metrics, you can end up chasing a less desirable audience. You may also run the risk of alienating loyal subscribers with gimmicky and irrelevant content.

Stay focused on your brand's voice and values while making small changes that will lead to big results over time.

ABT: Always Be Testing

Testing allows you to fine-tune your newsletters and optimize your performance. Even a small percentage point increase in open rate can have a huge overall impact on a larger audience.

Moreover, A/B testing is not a one-time thing. Tastes change, and what works today might not work tomorrow. Make testing a regular part of your email campaign management.

How Should I Choose My Subject Lines To Test?

What are good subject lines for emails? As you try out different versions, learn what motivates your audience to click. 

4 Twists for Testable Subject Lines

You can start by testing out these four elements.

Experiment with Word Count

The ideal subject line length is around 7-9 words and 28-50 characters.

Start there and make subtle tweaks to find your perfect sweet spot.

Play With Language

It's important to match the tone of your subject line to the tone of your content and your brand voice.

But within that scope, you can play. You can try a humorous or playful approach, incorporate pop culture references, or try alliteration. You might be surprised to see what resonates with your audience.

Use Emojis

Thoughtful emoji use in subject lines can boost your open rates significantly. They're not right for all brands or communications, but the use of emojis correlates to higher open, click-through, and conversion rates.

In one study, emoji use resulted in almost 65% higher click-through rates (CTRs).

Use only one emoji per subject line and stick to those directly related to your subject line content. Using an emoji just for the sake of it likely won't significantly impact your open rate.

Appeal to Different Drives

How can you best create desire? Try different subject-line strategies.

Tell your audience what they will gain by opening your email. Hint at exclusive content, instill a sense of community, or promise to teach them something new.

Keep testing different approaches to see what drives your audience to open and read.

Learn What Your Audience Prefers

Drive your audience engagement to new heights. Get started with A/B testing to learn about your audience and fine-tune your strategies.

Don't be afraid to experiment. The beauty of testing lies not in perfection, but in continuous improvement.

And if you want more detailed A/B testing ideas, take a look at this article from Michael Comeau. Let him tell you what he learned from conducting more than 1,000 tests.