If you’re not split testing your Klaviyo campaigns, you’re leaving revenue on the table. At ASPEKT, we generate about $300,000 per month in email revenue for our clients, and a big part of that comes from structured, strategic A/B testing.

In this guide, I’ll walk you through:

• Why split testing is essential for email marketing.

• The exact process to set up a test inside Klaviyo.

• The key variables we test (and which ones to avoid).

Let’s dive in.

Why Split Testing Matters

Split testing (or A/B testing) is the most reliable way to find out what works with your audience. But here’s the catch: you can only test one variable at a time.

If you test subject line, send time, and content all at once, you’ll never know which factor actually drove the results. Sticking to one variable ensures your data is clean and actionable.

The other critical piece is statistical significance. If your list is under 1,000 contacts, you probably won’t see meaningful results. Once you cross that threshold, your data becomes reliable enough to guide decision-making.

How to Set Up an A/B Test in Klaviyo

Here’s a step-by-step breakdown of how we run tests in Klaviyo:

1. Create a Campaign. Name it and choose your audience (ex: newsletter subscribers).

2. Add Your Content. Choose an email template and fill in subject line, preview text, and sender name.

3. Enable A/B Test. At this stage, Klaviyo allows you to create multiple variations.

   • Variation A: Subject Line A

   • Variation B: Subject Line B
     (You can also change preheader text, sender name, or email content if that’s the variable you’re testing.)

4. Choose Your Goal. Decide what you want to optimize for:

   • Open rate → Best for subject line and send time tests.

   • Click rate → Best for CTA and content tests.

   • Revenue rate → Best for offers and promotions (requires larger lists).

5. Adjust Distribution. Klaviyo lets you split your audience. A common setup:

   • 25% get Variation A

   • 25% get Variation B

   • The winning version (based on open or click rate) automatically goes out to the remaining 50%.

6. Set Test Duration. Typically 4 hours is enough to collect reliable open and click data (if sending during the day).

Pro Tip: Avoid optimizing directly for revenue unless you have a very large list. Attribution can be delayed and results may look “off” compared to engagement metrics.

Our Go-To Email Tests

Here are the core tests we run for clients that consistently deliver insights and revenue lift.

1. Subject Lines

Subject lines are the number-one driver of open rates. If subscribers don’t open, they’ll never click or buy. Test things like:

• Curiosity-driven vs. straightforward copy.

• Short vs. long subject lines.

• Personalization (name, location, behavior).

2. Send Time

When you send is just as important as what you send. Hitting the inbox at the right moment can mean the difference between a delete and a click.

Klaviyo offers Smart Send Time Testing, which helps identify your audience’s most responsive hours. After about two weeks, it can recommend the best time window to maximize engagement.

3. Call-to-Action (CTA)

Once subscribers open your email, the CTA drives them to act. Small tweaks can dramatically affect click-through rate.

Things to test:

• Button text (e.g., “Shop Now” vs. “See What’s New”).

• Button color or style.

• Placement (top, middle, bottom of the email).

4. Offers

Discount structure can make or break a campaign’s revenue. Testing different offers reveals what resonates most.

Examples:

• Free shipping vs. 10% off.

• Dollar-off discounts vs. percentage-based discounts.

• Buy one, get one (BOGO) vs. cashback incentives.

5. Text-Only vs. Designed Templates

Sometimes the best-performing emails aren’t the prettiest. We regularly test plain-text style emails (that look like a personal note) against branded, image-heavy templates.

Surprisingly often, plain-text wins, especially for relationship-driven or founder-style messages.

Best Practices for A/B Testing

To maximize the impact of your tests, follow these rules of thumb:

1. Test One Variable at a Time. Never test subject line, content, and send time together. Keep it clean.

2. Ensure Statistical Significance. Aim for at least 1,000+ recipients in your sample size. Larger lists give more reliable results.

3. Run Tests Long Enough. Give each test 3-4 hours (minimum) during active hours, or longer if your list is smaller.

4. Iterate. Use winning results as your new control, then test again. Testing is a cycle, not a one-off event.

Common Mistakes to Avoid

Even experienced brands fall into these traps:

• Over-testing: Running dozens of small tests that don’t move the needle. Focus on the variables that impact opens, clicks, and purchases most.

• Misinterpreting Results: Declaring winners too early without enough data. Always wait until you’ve reached significance.

• Testing Revenue Too Soon: With small lists, optimizing for revenue can mislead. Focus on open and click rates first, then layer in revenue testing once you scale.

Final Thoughts

Split testing is one of the fastest ways to improve your Klaviyo campaigns. By focusing on the right variables, subject lines, send times, CTAs, offers, and templates, you’ll gather actionable insights that compound over time.

The brands we work with that commit to regular, structured testing see steady lifts in open rates, click-through rates, and ultimately revenue.

If you’d rather not spend weeks figuring this out on your own, our team at ASPEKT can set up and optimize your A/B tests for you. Book a free Klaviyo audit and we’ll show you exactly where to start.