Your subject line is the gatekeeper. It does not matter how brilliant your email body is if nobody opens the message. In B2B cold email, the average open rate hovers around 20 to 25 percent. Top performers consistently hit 40 to 60 percent. The difference is almost always the subject line.
After analyzing open rate data from thousands of cold email campaigns, we have identified the subject line patterns that consistently outperform. You can also use our email subject line generator to create tested subject lines instantly. This guide gives you 50 ready-to-use templates organized by category, along with the psychology behind why each type works and when to use it.
The Science Behind High-Performing Subject Lines
Before we get to the templates, it helps to understand what makes a subject line work. Research on email engagement reveals several key principles:
- Shorter is better: Subject lines with 6 to 10 words have the highest open rates. Mobile devices truncate anything over about 40 characters.
- Personalization lifts performance: Including the recipient's company name or a specific detail increases open rates by 20 to 30 percent on average.
- Curiosity outperforms clarity in cold email: Unlike marketing emails where clarity wins, cold emails benefit from creating an information gap that the recipient wants to close.
- Lowercase and casual tone: Subject lines that look like they came from a colleague rather than a marketing department get opened more often.
- Avoid spam triggers: Words like "free," "guaranteed," "act now," and excessive punctuation send emails straight to spam.
Category 1: Question-Based Subject Lines
Questions create an open loop in the reader's mind. They want the answer, so they open the email. These consistently produce open rates in the 35 to 50 percent range.
- 1. "Quick question about [Company Name]'s [process]"
- 2. "[Name], who handles [function] at [Company]?"
- 3. "Struggling with [specific challenge] too?"
- 4. "Is [Company Name] still using [old approach]?"
- 5. "What would 30 percent more [metric] mean for [Company]?"
- 6. "Curious -- how does [Company] handle [process]?"
- 7. "[Name], have you considered [alternative approach]?"
- 8. "Still looking for a better way to [achieve outcome]?"
Category 2: Personalized and Research-Based Subject Lines
These subject lines demonstrate you have done your homework. They work because they stand out in a sea of generic mass emails. Open rates typically range from 40 to 55 percent.
- 9. "Saw [Company]'s recent [news/announcement] -- had a thought"
- 10. "Congrats on [achievement] -- quick idea"
- 11. "Your [LinkedIn post / talk / article] got me thinking"
- 12. "Noticed [Company] is hiring for [role] -- relevant timing"
- 13. "[Mutual connection] suggested I reach out"
- 14. "Fellow [industry / alma mater / city] connection"
- 15. "Loved your take on [topic] at [event]"
Category 3: Value-First Subject Lines
These lead with a benefit or outcome that the prospect cares about. They work because they immediately answer the question "what is in it for me?" Open rates range from 30 to 45 percent.
- 16. "Idea to help [Company] [achieve specific outcome]"
- 17. "How [similar company] increased [metric] by [X] percent"
- 18. "[X] ways to [solve problem] without [common pain]"
- 19. "A resource for [Company]'s [initiative]"
- 20. "Saving [Company] [time/money] on [process]"
- 21. "Cut your [process] time in half -- here is how"
- 22. "[Competitor] is doing this -- thought you should know"
Category 4: Short and Intriguing Subject Lines
Sometimes less is more. Ultra-short subject lines create maximum curiosity. They look like internal emails, which makes them hard to ignore. Open rates range from 35 to 50 percent, but reply rates may be lower because the email body has to work harder to establish relevance.
- 23. "Quick thought"
- 24. "[Company Name]"
- 25. "Idea for you"
- 26. "[Name] -- 2 min?"
- 27. "Timing"
- 28. "For [Name]"
- 29. "Re: [Company] growth"
- 30. "Thoughts?"
Category 5: Social Proof Subject Lines
These leverage the power of association. When a prospect sees that similar companies or known brands are getting results, it creates both credibility and FOMO. Open rates range from 30 to 45 percent.
- 31. "How [known company in their industry] books 40 meetings/month"
- 32. "What [X] [industry] companies are doing differently"
- 33. "[Number] of your peers are already doing this"
- 34. "[Known company] switched from [old way] -- here is why"
- 35. "Case study: [Company] achieved [result] in [timeframe]"
- 36. "Why [industry] leaders are investing in [approach]"
Category 6: Follow-Up Subject Lines
Follow-up emails are where most deals are won. These subject lines keep the conversation going without being pushy. Open rates on follow-ups are typically 10 to 20 percent lower than initial emails, but these templates close the gap.
- 37. "Following up -- [one-line value reminder]"
- 38. "Did this land at the right time?"
- 39. "Bumping this -- still relevant?"
- 40. "One more thing about [topic from first email]"
- 41. "[Name], any thoughts on this?"
- 42. "Closing the loop on [topic]"
- 43. "Not trying to be a pest -- last note"
Category 7: Breakup Subject Lines
The breakup email is the final touch in a sequence. Ironically, it often gets the highest reply rate because it removes pressure and creates urgency. Open rates are often 35 to 50 percent.
- 44. "Should I close your file?"
- 45. "Permission to close the loop?"
- 46. "Is this a dead end?"
- 47. "Last attempt -- then I will stop"
- 48. "Breaking up is hard to do"
- 49. "Not a fit? No worries."
- 50. "Going, going..."
Subject Line Testing Best Practices
Having great templates is only the starting point. You need to test and iterate continuously. Here is how to run effective subject line tests:
- Test one variable at a time: If you change the subject line and the body copy simultaneously, you will not know what caused the difference in performance.
- Use sufficient sample sizes: You need at least 100 sends per variant to get statistically meaningful results. Ideally 200 or more.
- Measure beyond open rates: A subject line that gets opened but does not lead to replies is not useful. Use our cold email grader to evaluate the full message, and track the full funnel -- opens, replies, meetings booked.
- Segment your tests: What works for C-level executives may not work for directors. What works in fintech may not work in healthcare. Test by persona and industry.
- Rotate subject lines: Even great subject lines fatigue over time, especially if you are emailing into the same market. Refresh your templates every 4 to 6 weeks.
Common Subject Line Mistakes to Avoid
- All caps or excessive capitalization: "INCREASE YOUR REVENUE BY 300%" screams spam
- Misleading "Re:" or "Fwd:": Using fake reply or forward indicators is deceptive and damages trust instantly
- Being too clever: Puns and wordplay that require thought to understand lower open rates because the recipient does not have time to decode your joke
- Including your company name: Save the introduction for the email body. Your subject line real estate is too valuable to waste on a name they do not recognize yet.
- Being too long: If it gets cut off on mobile, it is too long. Keep it under 40 characters whenever possible.
At Dewx.io, we test subject lines relentlessly across every cold email campaign we run. The difference between a 20 percent open rate and a 50 percent open rate compounds across thousands of emails into a massive difference in pipeline generated. Start with these 50 templates, test aggressively, and let the data guide your evolution.