Can preheader text be A/B tested?

You've probably spent time crafting the perfect subject line, but there's a second line of text sitting right next to it in every inbox. That's your preheader, and yes, it's absolutely worth testing.

Preheader text is the short preview that appears after the subject line in Gmail, Outlook, Apple Mail, and most other clients. On mobile especially, it's the first thing people see before they decide to open. Ignoring it is like writing a great headline and leaving the subhead blank.

The most common mistake senders make is not setting a preheader at all. When that happens, the inbox just pulls the first line of body copy, which is often "View this email in your browser" or some other piece of technical boilerplate. That's wasted space.

When you do test preheaders, these are the variations worth trying:

• Complement vs. repeat. Does adding new information (complementing the subject) outperform restating it in different words?
• Teaser vs. summary. Does hinting at what's inside beat spelling it out upfront?
• Call to action vs. benefit statement. "Get 20% off today" vs. "Your exclusive discount is waiting."
• Personalized vs. generic. "Hey marina@deepcurrent.io, your order is ready" vs. a one-size-fits-all preview.

The subject line and preheader work as a pair. Testing them separately is useful, but the real gains come from treating them as a system and finding combinations that click together. A strong subject plus a weak preheader underperforms. A strong subject plus a strong preheader can meaningfully move your open rate.

Open rate is your primary metric here. But don't stop there. Check whether higher opens from a particular preheader variant also lead to better click-through and conversion. Sometimes a teaser line drives opens out of curiosity but the audience isn't primed to act once they're inside.

Want to stress-test your subject and preheader pairing before you send? Our free Subject Line Tester can help you spot obvious issues before the campaign goes out.