A/B Test Email Subject Lines: 10 Steps

Want to boost your email open rates? A/B testing subject lines is key. Here's a quick guide:

Set clear goals (e.g., increase open rate by 5%)
Choose one element to test (length, personalization, etc.)
Create two versions of your subject line
Split your email list randomly
Determine sample size (aim for 1,000+ per variant)
Set up the test in your email tool
Send emails at the same time
Analyze results (focus on open rates, clicks, conversions)
Pick a winner based on statistical significance
Apply insights and keep testing

Remember:

Test one thing at a time
Use similar test groups
Wait for solid results before deciding

Element	Why It Matters
Open rate	Shows subject line appeal
Click-through rate	Indicates content relevance
Conversion rate	Measures email effectiveness

A/B testing isn't a one-time thing. Keep at it to improve your email marketing over time.

1. Set Your Goal

Before diving into A/B testing email subject lines, you need a clear target. It's not just about trying different options - it's about boosting your email performance in ways that matter.

Pick Key Metrics

Focus on numbers that show real impact. For subject lines, these usually include:

Open rate
Click-through rate (CTR)
Conversion rate

Let's say you run an online store. Your current email campaign looks like this:

20% open rate
5% CTR
2% conversion rate

You might aim to bump that open rate to 25% with better subject lines.

Match Goals to Business Needs

Make sure your test aligns with your overall business strategy. Ask yourself:

What's not working in our current email approach?
How can better subject lines fix this?
What improvement would actually move the needle?

Here's a real-world example:

A daily newsletter was struggling with a 12% open rate, way below their 25% target. The team decided to A/B test subject lines to boost engagement and hit their Q3 goals.

Current Performance	Goal
12% open rate	25% open rate

Each test is a chance to understand your audience better and level up your emails. Start with clear goals, and you'll get clearer results.

2. Pick What to Test

You've set your goals. Now, let's choose what to test in your email subject lines. The key? Test one thing at a time.

Subject Line Elements to Test

Some popular options:

Length: Short vs. long
Personalization: Name or no name
Emojis: Use them or not
Tone: Professional or casual
Urgency: Create FOMO or keep it chill

Focus on High-Impact Tests

Pick tests that match your goals and could make a big difference. For example:

If you want to boost open rates, try testing:

Test	Version A	Version B
Personalization	"Your weekly update"	"John, your weekly update"
Urgency	"New products added"	"24 hours left: New products"

Test one element at a time. This way, you'll know exactly what caused any changes.

"A subject line test is simple: Send the same email to small groups. See which one gets more opens, then use the winner for everyone else."

Real-world examples:

1. Urgency Test

A furniture retailer tested dynamic subject lines in cart abandonment emails. They included the product name to remind shoppers of what they browsed.

2. Question vs. Statement

Dermstore tested:

"Take Them Home..."
"Did You Forget Something?"

3. Length Test

Pura Vida compared:

"It's Back!"
"You wanted it and now it's back!"

3. Make Test Versions

Time to create your subject line variations. Let's craft options that'll give you clear, useful results.

Write Subject Lines

Focus on the element you're testing. For personalization, it might look like this:

Version A	Version B
"Your weekly update"	"John, your weekly update"

We're only changing the personalization here. That's key.

Tips for effective test versions:

Be clear
Use action words
Create urgency (if it fits)
Ask questions
Use numbers

"Use 'Q3 Report: Key Insights and Trends' instead of 'Update.'" - Oren Todoros, Head of Content Strategy at Spike

Keep Other Parts the Same

ONLY change the subject line. Everything else stays the same:

Email body
Sender name
Send time
Images and formatting

This ensures any performance differences come from the subject line alone.

Testing subject line length? Here's how:

Element	Version A	Version B
Subject	"24-hour sale starts now!"	"Don't miss out: Our biggest sale of the year is happening right now, for 24 hours only!"
Body	[Same content]	[Same content]
Sender	"YourStore Team"	"YourStore Team"
Send time	Tuesday, 10:00 AM	Tuesday, 10:00 AM

4. Split Your Email List

Splitting your email list is crucial for A/B testing. Here's how to do it right:

How to Split Your List

For most tests, a 50/50 split works fine. Half your list gets version A, half gets B.

Got over 1,000 contacts? Try a 10/10/80 split:

Group	%	Purpose
A	10%	Test
B	10%	Test
C	80%	Gets winner

This lets you test small, then send the winner to most of your list.

Random Assignment is Key

Random assignment prevents bias. Here's a quick Excel method:

Export your list
Add a "Random Number" column: =RAND()
Label groups: =IF(A2>=0.5, "A","B")
Sort by random number
Copy groups to new files

"Random assignment ensures test differences come from your changes, not group makeup." - Email Marketing Quarterly, 2023 Q2 Report

Aim for at least 1,000 contacts total, with 100+ expected conversions. Smaller list? Test anyway, but be careful about conclusions.

5. Choose How Many to Test

Picking the right sample size is crucial for reliable A/B test results. Here's what you need to know:

Why Sample Size Matters

Small samples can lead to false positives. Larger samples give more trustworthy results.

Here's a quick guide:

List Size	Minimum Test Size
< 1,000	50% of your list
1,000-10,000	1,000 per variant
> 10,000	5,000 per variant

Aim for at least 1,000 emails per test group. With smaller lists, test a larger percentage.

Tools for Accuracy

Don't guess. Use these:

A/B Test Calculators
Email Marketing Platform Tools

Using an A/B test calculator:

Enter current open rate
Choose minimum detectable effect (usually 5%)
Set confidence level (95% standard)
Get your sample size

"With a segment of 4,000 people, running an A/B test may yield only 76% certainty that one subject line is an improvement over another, indicating a p-value of 24%." - Email Marketing Quarterly, 2023 Q2 Report

This shows why bigger samples matter. For 95% confidence, you'd need more than 4,000 emails.

Got a list under 50,000? You might struggle to get solid results. Test anyway, but be cautious about big decisions based on the outcomes.

6. Set Up Your Test

Here's how to set up your A/B test for better email subject lines:

Pick a Good Email Tool

You need an email service that makes A/B testing a breeze. Look for:

Built-in A/B testing
Easy setup
Multiple variable testing
Clear results

Some top tools:

Tool	Best For	Top Feature	Cost
ActiveCampaign	Customization	5 test versions	Varies
Benchmark	Small businesses	Campaign comparisons	Free plan
MailChimp	Comprehensive testing	List segmentation	Free basic

Follow Setup Steps

1. Create your test

Hit "Create" or "New Campaign"
Pick "A/B Test"
Name it

2. Choose what to test

One variable (like subject line)
Make 2-3 versions

3. Set test parameters

Audience size (1,000+ per version)
Duration (2 weeks is good)
Winning criteria (open rate, clicks)

4. Add your content

Write email body
Create subject line versions

5. Review and launch

Check all settings
Send yourself a test
Hit launch

Remember: You need at least 1,000 subscribers for solid results. Smaller list? Test a bigger chunk of your audience.

"To create a new A/B test, click the Create icon, then click Email. Next, click A/B test. Enter an email name and click Begin." - MailChimp's A/B Testing Guide

7. Run Your Test

It's go time! You've set up your A/B test, now let's launch and keep an eye on it.

Send at the Same Time

Timing is everything. Send all test emails at once to avoid messing up your results.

Why? It:

Cuts out time-based biases
Lets you compare versions fairly
Stops seasonal changes from throwing things off

Pro tip: Pick a send time when your audience is most likely to open emails. Check your email platform's data to find the sweet spot.

Watch Early Results

Keep tabs on how people react right after you hit send. Early data can tell you a lot.

What to look at:

Open rates
Click-through rates
Unsubscribe rates

Metric	Why It Matters	What to Watch For
Open rates	Shows if subject lines work	Big changes up or down
Click-through rates	Tells if content hits the mark	Differences between versions
Unsubscribe rates	Shows overall email quality	Any weird spikes

Don't jump to conclusions too fast. Let the test run its full course for solid data.

Here's a real-world win:

"We A/B tested send times for our newsletter and saw a 9.3% increase in opens and a 22.6% boost in clicks", says Kevan Lee, Buffer's Content Marketing Manager.

Keep everything the same except your test variable (the subject line). This means:

Email content
Sender name
Send time
List segments

Consistency is key for accurate results.

8. Look at Results

Your A/B test is done. Time to dig into the data.

Key Metrics to Focus On

Metric	What It Shows
Open rate	Subject line's appeal
Click-through rate (CTR)	Content matching subject line
Conversion rate	Email driving desired action

Compare A and B versions side by side. Example:

Subject line A: 25% open rate Subject line B: 30% open rate

B wins for attention. But did it lead to more clicks and conversions?

Statistical Significance

Raw numbers can mislead. Use a statistical significance calculator to ensure your results matter.

Why it's crucial:

Confirms if A/B difference is real
Prevents decisions based on chance
Boosts confidence in applying findings

Aim for 95% statistical significance or higher. If you fall short:

Run the test longer
Increase sample size
Make bigger subject line changes

"The closer your p-value is to zero, the more certain your results aren't coincidental." - Cassie Kozyrkov, Google's Chief Decision Scientist

Even small gains count. A 5% open rate boost can mean thousands more readers for big lists.

Keep testing. Each A/B test teaches you how to make your next email better.

9. Make Decisions

After your A/B test, it's time to pick a winner and use your results.

Choose the Winner

Look at your key metrics to decide which subject line did better:

Metric	What It Shows
Open rate	Interest in the email
Click-through rate	Engagement with content
Conversion rate	Action taken

Pick the subject line that fits your goals. Want more opens? Go for the higher open rate. Aiming for sales? Choose the better conversion rate.

Check the Math

Don't trust raw numbers alone. Use a statistical significance calculator to make sure your results aren't just luck.

Aim for 95% confidence. This means only a 5% chance your outcome was random.

If you don't hit 95% confidence:

Run the test longer
Test with more subscribers
Make bigger changes to subject lines

Even small gains count. A 5% open rate boost can mean thousands more readers for big lists.

"Only 1 in 8 A/B tests produces significant results", says Klaviyo's research.

This shows why you should:

Test often
Be patient
Look for real differences

Once you have a winner, use what you learned in future emails. Keep testing to find what works for your audience.

10. Use Results and Keep Testing

After your A/B test, it's time to put the results to work and keep improving.

Use What Worked

Take the winning elements and apply them to future campaigns:

Winning Element	Next Steps
Emoji in subject	Add emojis to more subjects
Question format	Ask questions in future emails
Discount mention	Highlight offers in subjects

Don't stop at one test. Keep using what you learn to make your emails better.

Always Improve

Email marketing evolves quickly. What works today might not work tomorrow. So, keep testing.

Here's how ongoing testing boosted results for some companies:

River Island cut down on emails but made each one count more. They saw a 30.9% jump in revenue per email and got 30.7% more orders per email.

Whisker tested using the same message across different campaigns. This led to a 107% increase in conversion rate and 112% more revenue from users who saw the repeated message.

Pro tip: Test one thing at a time. This helps you pinpoint what caused any changes in your results.

Even small gains add up. A 5% boost in open rate could mean thousands more readers for big email lists.

Keep an eye on trends too. About half of shoppers like weekly emails from brands they love. And half of those people buy something from marketing emails at least once a month.

Conclusion

A/B testing email subject lines can supercharge your email marketing. Here's a quick rundown of the 10 steps to run effective tests:

Step	Action
1	Set goals
2	Pick test element
3	Create versions
4	Split list
5	Choose sample size
6	Set up test
7	Run it
8	Check results
9	Make decisions
10	Apply and repeat

A/B testing isn't a one-and-done deal. It's an ongoing process that helps you understand what makes your audience tick.

Keep these in mind:

Test one thing at a time
Use similar test groups
Send emails simultaneously
Wait for solid results

Make A/B testing a habit, and you'll see your email game improve. Even small wins can add up to big results.

"If people are unwilling to open the emails you send them, the rest of your marketing campaign is simply going to fall flat." - Mailchimp

This quote nails it. Your subject line is your first impression. Nail it, and you're halfway there.

So, what are you waiting for? Start testing those subject lines and watch your email marketing take off.

FAQs

How to A/B test email subject lines?

Want to boost your email marketing? A/B test your subject lines. Here's how:

1. Choose one element to test

Pick ONE thing to change. For subject lines, try:

Adding the recipient's name
Mentioning product details
Using a question instead of a statement
Short vs. long subject lines

2. Write two versions

Create two subject lines. Only change the element you're testing.

3. Split your list

Divide your email list into two random groups.

4. Send and compare

Send each version to its group at the same time. Look at open rates to see which won.

Here's a real-world example:

Version A	Version B	Result
"New summer styles just in!"	"Sarah, check out our new summer collection"	Version B: 15% higher open rate

Don't stop at one test. Keep experimenting to improve your emails.

"Only about 61 percent of marketers use A/B testing to improve their marketing performance."

A/B Test Email Subject Lines: 10 Steps