Subject Line A/B Testing Techniques and Examples in Email Marketing

Ever wondered why some emails grab your attention while others vanish into the inbox void? You may not know, but 64% of people decide to open emails based on the subject line alone. The most interesting part is, 69% of recipients report emails as spam just from glancing at the subject. 

But how do you create subject lines that not only avoid the spam folder but also drive real results? Enter the world of A/B testing, your secret weapon for email marketing success. Let’s dive into the art and science of crafting subject lines that get opened and drive action with A/B testing.

The Magic of Subject Lines in Email Marketing

First impressions matter

People say not to judge a book by its cover; however, in real life, the cover is sometimes all that matters. Like a book cover, if your subject line doesn’t grab attention, nobody cares what you have on the inside. It is the first (and sometimes only) thing recipients see. As such, it is arguably the most important part of your email. 

With recipients spending mere seconds evaluating subject lines, yours needs to be compelling and relevant. Moreover, subject lines play a crucial role in email organization, influencing whether your message lands in the priority inbox or gets filtered as spam. 

A/B testing: Your ticket to being heard

While subject lines work magic by helping you grab attention and increase open rates, there is no exact one-size-fits-all formula for everyone. Yes, there are general principles; however, the application of these principles might vary slightly. The reason is, every marketer has a specific audience, and every type of audience has something that resonates with them. 

For instance, while discounts might catch the attention of students, the catchy subject line for a luxury fashion brand might be new arrivals or something in that direction. In other words, you need to find out what works for you and your unique audience. This is where A/B testing comes in. 

Essentially, A/B testing is sending out two variants of the same message while you test the performance to determine which suits you best. By testing different versions of your subject lines, you can uncover what your readers really want. You are not trying to get lucky; instead, you are deciding your own fate with data-driven decision-making at its finest.

The curiosity gap and emotional punch 

Have you seen an interesting movie that you didn't finish? You know, that irresistible urge to go back and find out what happens in the end—that urge is called the curiosity gap. 

George Loewenstein’s information-gap theory defines the curiosity gap as a cognitive drive, similar to hunger, that arises when we perceive a gap in our knowledge. In email marketing, this translates to the space between what your subject line reveals and what it does not say. 

By strategically creating this gap with your subject line, you pique the reader’s interest, compelling them to open the email to satisfy their curiosity. Combine this with emotional triggers—words that evoke excitement, urgency, or even fear of missing out—and you have a powerful formula. 

Open sesame: The impact on open rates 

If you are having issues with low open rates, the big problem might be your subject line. In a recent study, researchers discovered that well-crafted subject lines—personalized, emotion-eliciting, and concise—significantly outperformed standard ones. The best performers had open rates increase by up to 26%. How cool is that?

Brand perception: More than just words 

Your email open rate is a great metric to measure; however, your subject line does a lot more for you. Beyond the allure of compelling people to open your emails, your subject line acts as a brand ambassador for your amazing brand. With a properly crafted subject line, you are essentially shaping how people see your brand. 

When you give people what they want to see, they become hooked on your messages, like it’s an interesting serial. With creativity on your side, you can build an amazing relationship with your readers, one email at a time.

Key Elements of a Subject Line to Test (With Examples)

Let’s explore the key elements to test in your subject lines. 

Clever vs. clear

Sometimes, being clever helps you win hearts. Other times, clarity trumps creativity. However, only testing can tell you which one your audience prefers.

Here is an example of clever vs. clear: “Unbox happiness today!” vs. “New product launch: 20% off.” While the first one is witty, the second one explains what to expect in the email.

Long vs. short

While many experts say around 70 characters is ideal to get the attention of your readers, there are debates about the exact length that gets the highest open rates. The following image shows a research that attempts to show that about 20 characters is just ideal. 

The difference in these results shows that you need A/B testing to know whether your audience prefers detailed previews or quick, punchy messages. 

Try: “Last chance: Our biggest sale of the year ends at midnight!” vs. “Flash sale: 24 hours left!”

Questions vs. statements

Questions can engage the mind, but statements can convey authority. Which works best? You guessed it—test it!

Compare: “Ready to revolutionize your workout?” vs. “New fitness gear just dropped!”

Personalization vs. no personalization

Studies show that personalization increases open rates by up to 26% across most industries. However, in some industries, like publishing, the difference in open rate is almost close to zero. So, do not just assume; test and see what works for your audience. 

When it comes to personalization, there is a lot to test. Consider the following for a start:

• Name vs. no name: “Sarah, your cart misses you!” vs. “Don’t forget about your cart!”
• First name vs. last name.

Tone and style

Your brand voice matters, so test your subject line to see how it matches your overall tone. One way to do this is to check the formal vs. informal tone/style. 

• Formal: “Exclusive Offer for Our Valued Customers.”
• Informal: “Psst… Here’s a deal you can’t refuse!”

Urgency and scarcity

FOMO (fear of missing out) is real. But how much urgency is too much? Testing will reveal the sweet spot.

Try: “Only 5 spots left—book now!” vs. “Join our upcoming webinar!”

Emojis

Emojis in email subject lines can significantly impact open rates, but results vary by industry and audience. 

While some studies show increased engagement, others found decreased open rates. It’s crucial to test emoji usage with your specific audience to determine effectiveness.

Numbers and lists

Numbers can add specificity and structure. But do they always work? You know the drill—test it out!

Compare: “5 ways to boost your productivity” vs. “Boost your productivity today!”

A/B Testing Techniques for Subject Lines

Formulate your hypothesis

A test without a goal is like sailing without a destination—you might move, but you won’t know if you’re making progress.

So, before you start testing, have a clear idea of what you’re testing and why. A hypothesis can look like this: “Including an emoji will increase open rates by 10%.”

Segment your audience

Split your email list into random, equally-sized groups. Remember, the larger the sample size, the more reliable your results will be. 

Aim for at least 1,000 recipients per variation for statistically significant results. Statistically significant means the best email really performed better and was not merely due to chance.

Run the test

Send your emails at the same time to eliminate variables like the day of the week or time of day. Keep everything else in the email identical except for the subject line you’re testing. Sending emails on different days or at different times means you are testing the effect of the time or day in addition to the subject line. 

Analyze the results

Now that you have done your test, you need to carefully check the results. Yes, open rate is a great metric, but your evaluation should not stop there—look beyond just open rates. Click-through rates and conversion rates are also important metrics that can tell you if your subject line set the right expectations for the email content.

Common Mistakes to Avoid

Testing too many variables

Testing too many things at once is like trying to catch multiple balls while juggling blindfolded—you’re likely to miss them all and won’t know which one you actually caught.

Yes, you got an increased open rate of 40%—great! Now, which of the variables actually contributed to that 40%? It’s hard to tell because you tested too many things at once.

So, instead, stick to one variable at a time. That way, you can tell which element makes the biggest difference.

Insufficient sample size

Getting a 60% open rate might seem like an achievement until you discover the audience was 10 people. When you think of it, 6 people clicking your email out of 10 might just be an error. However, if 60% of 1,000 people click the email—that’s something because 600 people cannot make the same mistake at a time. So, ensure your test groups are large enough for meaningful results. 

Ignoring context

Consider external factors like holidays, current events, or industry trends that might impact your results. For instance, if you send emails on a weekend, there is a possibility that people might not read them like on a weekday. So, factor that in as well.

To Sum Up

When you write your emails, you should ask yourself this important question: Are you simply writing and leaving it all to chance, or are you making data-driven decisions with your subject line? The answer to that question will depend on whether you use A/B testing. 

A/B testing will help you refine your subject lines and improve open rates while building a stronger connection with your customers.

Remember, there’s no one-size-fits-all solution. What works for one brand might flop for another. The key is to keep testing, keep learning, and keep refining. Your perfect subject line is out there—you just need to discover it.

So, are you ready to revolutionize your email marketing? (Did you see that? That’s a testable subject line right there!) Start A/B testing your subject lines today and watch your email performance soar. Your inbox will thank you, and more importantly, so will your audience.