Identify best practices for A/B testing
Before we dive into email-specific strategies, refresh your memory on general A/B testing best practices to ensure you’re conducting effective tests.
Get inspired: Top elements to test in emails
As a reminder, it’s imperative that you only test 1 element of your email per A/B test. That leads to the question: which element should you test now to make the biggest impact?
Click into the dropdowns below to explore common email elements you may A/B test to see what truly drives your subscribers to act.
Subject line
Your subject line acts as a first impression; it determines whether an email gets opened or ignored. Even small changes can significantly impact open rates, which directly affects how many people can then convert from your email.
What to test:
- Different phrasing: For instance, pose a question vs. lead with an action verb (e.g., “Ready for your next fashion statement?” vs. “Make a fashion statement.”)
- Adjust length: Does a longer or shorter subject line drive opens?
- Test the impact of urgency: Does adding urgency, or comparing different levels of urgency, impact your subject line? (“Shop now, while supplies last” vs. “Only 30 left in stock, it’s time to act fast.”)
- Test the value of emojis: Does an emoji draw the eye or disuade someone from clicking?
- Add personalization: Does adding in someone’s first name affect open rate?
Test value propositions: Determine what value proposition drives results (e.g., “Shop now, see clearer skin in days.” vs. “Shop now, and your skin glow.”
Hook and tone
Once the email is opened, the hook determines whether the reader keeps going. Tone influences how the brand is perceived and how well a message resonates with different audiences. Testing this can help you find the voice that converts attention into action.
What to test:
- Opening lines (e.g., the “hook” that draws someone in immediately);
- The tone of your email (e.g., playful vs. direct vs. informative).
- Small adjustments or changes to your brand voice.
- Your overall message framing (e.g., benefit-driven vs. storytelling).
Images and visuals
Visuals shape how quickly and effectively a message is understood. The right imagery can increase engagement and clarity, while the wrong visuals can distract readers, slow them down, and even cause rendering issues. Testing helps identify what best supports conversion rather than just aesthetics.
What to test:
- Lifestyle vs. product imagery
- GIFs vs. static images
- Image placement (e.g., where it lives in email, whether its in line with text, full email width, etc.)
- Amount of imagery (e.g., does having 1, 2, or even no images affect the conversion rate of an email?)
Incentive structure
Incentives can directly impact purchase motivation, but offering too much erodes margins. A/B testing helps brands find the balance between maximizing conversions and protecting profitability, ensuring sustainable growth rather than short-term spikes.
What to test:
- Discount amounts (10% vs. 20%)
- Dollar vs. percentage discounts ($10 off vs. 10% off)
- Free shipping vs. discount
- Bundles vs. free item
- Tangible discount vs. no incentive, emphasis on value proposition
Personalization
Personalization increases relevance. Emails that feel tailored to the recipient tend to perform better because they align with individual interests and behaviors. Testing reveals how much personalization actually drives lift versus adding unnecessary complexity.
What to test:
- Product recommendations (e.g., do static best sellers or dynamic recommendations perform better for first time shoppers?)
- Behavioral data (e.g., based on someone’s expected lifetime CLV, how do different levels of discounts perform via email?)
- Segment-specific messaging (e.g., do text-heavy blocks perform better across all segments; for instance, how do different age groups respond to this content)
Call-to-action design
Your CTA drives conversions. Even subtle changes can impact click rates and downstream revenue. Test your CTA to ensure that it is clear, compelling, and frictionless, guiding subscribers toward the desired action.
What to test:
- Button copy (“Shop Now” vs. “Get Yours”),
- Button placement within the email
- Button color
- Button size
- The number of CTAs in your email
Grow your A/B testing strategy over time
A/B testing is most powerful when it becomes part of an ongoing strategy. In Klaviyo, you can start with a standard winning variation test, then evolve to Personalized variations, where Klaviyo AI delivers the version each recipient is most likely to engage with based on their behavior, purchase history, and more. Instead of testing one message against another, you’ll identify which strategies resonate with specific customers and shift from batch-and-blast to intelligent lifecycle marketing.
Plus, to drive real growth, build a consistent testing cadence and focus on patterns over time. After each test, look beyond the winner and consider the full context, including your audience, timing, and goals. Then, repeat tests across different segments or lifecycle stages. Individual results can vary, but repeated insights lead to smarter, scalable decisions that improve relevance, customer experience, and overall performance.
Learn more about Personalized variations.