The numbers don't lie
47% of recipients open an email based on the subject line alone. The average open rate across industries is around 21%. The best subject lines consistently beat that — here's what they have in common.
Keep it short
Subject lines under 50 characters get higher open rates. On mobile, anything longer gets cut off. Aim for 6–10 words that create curiosity without giving everything away.
Create curiosity, not clickbait
The best subject lines hint at value without revealing it fully. 'The one thing we changed' beats 'We improved our onboarding process by 23%'. Curiosity drives opens; clickbait drives unsubscribes.
- 'A quick question about [topic]'
- 'The mistake most [industry] teams make'
- 'I thought of you when I read this'
- '[First name], this took us 3 months to figure out'
Use numbers and specificity
Numbers stand out in a crowded inbox. '5 ways to...' beats 'Ways to...'. Specificity signals that the email has real, actionable content — not fluff.
Personalize — but don't overdo it
Including the recipient's first name can lift open rates, but only when it feels natural. Over-personalized subject lines ('Hey Sarah, here's your exclusive offer!') feel manipulative. Use names sparingly and authentically.
Test everything
The only way to know what works for your audience is to test. A/B test subject lines on every campaign and let the data — not your gut — decide.
- Test one variable at a time (length, tone, personalization)
- Send to a small segment first, then roll out the winner
- Track open rates over time, not just on a single send
The takeaway
A great subject line is the highest-leverage 50 characters in your marketing. Write them carefully, test them relentlessly, and let the data guide you.