How to Write Email Subject Lines That Get Opened
The average inbox sees dozens of emails competing for attention every day. Your subject line has about 2 seconds to earn a click. All the work you put into writing a great email is wasted if the subject line doesn't clear that bar. Here's how to write ones that do.
What Makes Someone Open an Email
People open emails for a limited set of reasons: curiosity (what's in here?), self-interest (this is relevant to me), urgency (I need to act now), or trust (this person always sends value). The best subject lines trigger at least one of these. The weakest trigger none.
Subject Line Formulas That Consistently Work
| Formula | Example | Why It Works |
|---|---|---|
| Question | Are you making this SEO mistake? | Creates a curiosity gap |
| Specific number | 3 subject line mistakes I see every week | Specific = credible + curiosity |
| How to + outcome | How to double open rates this month | Clear self-interest signal |
| Threat/warning | This is silently killing your email list | Loss aversion is powerful |
| Personal direct | Quick question about your last campaign | Conversational = different |
| Curiosity gap | The email mistake I almost sent | Incomplete information drives opens |
Length and Format
Mobile devices truncate subject lines at 30–40 characters. Most inbox clients show 40–60 characters. Put the key message first. Emojis can work when they're relevant to your brand and used sparingly — one at the start or end of a subject line. Avoid using all caps (feels like shouting) or excessive punctuation.
Preheader Text: The Underused Second Chance
The preheader (the preview text shown next to the subject line in most inboxes) is the most underused real estate in email marketing. Most marketers leave it default ("View this email in your browser"). A good preheader text extends the subject line or adds additional context that increases the open rate by 10–20%.
What to Avoid
- Clickbait that doesn't deliver — Overselling in subject lines increases opens but increases unsubscribes and decreases trust long-term
- Vague subject lines — "Our latest newsletter" or "Check this out" tells the reader nothing
- Spam trigger words — "Free," "guaranteed," "100%," "act now" can affect deliverability
- Subject lines longer than 60 characters — The key message will be cut off on mobile
Testing Subject Lines
Most email platforms support A/B testing subject lines. Test one variable at a time: length, formula type, personalization, curiosity vs. direct. Send to 20% of your list in each variant, then send the winner to the remaining 60%. After 10–20 tests, patterns emerge about what your audience responds to.
FAQ
Do personalized subject lines (using the person's name) still work?
They can, but the effect has diminished as personalization has become common. Personalized subject lines work better when the rest of the email actually delivers personalized content. Using someone's name in a generic mass email can backfire by highlighting the lack of genuine personalization.
Should I use emojis in subject lines?
Test with your audience. Emojis can improve open rates when they're on-brand and used contextually. In B2B and professional contexts, they can feel out of place. In consumer brands, especially for younger audiences, they often work well. Never use an emoji that doesn't render correctly on all devices.
How do I know if my subject line is too promotional?
If it reads like an ad rather than a message from a person, it's too promotional. Imagine receiving it from a colleague rather than a company. Would it seem reasonable or salesy? Subject lines that feel like personal communication perform better than those that feel like broadcast advertising.
How much does subject line impact open rates?
Subject line is the dominant factor in open rate, alongside sender name and send time. A strong subject line can double open rates compared to a weak one on the same list. It's the highest ROI optimization in email marketing.
What's the best time to send emails to maximize opens?
Tuesday through Thursday, mid-morning (10am–11am) in the recipient's time zone is the conventional wisdom — and the data broadly supports it. However, your specific audience may differ. Enable send-time optimization if your platform offers it; over time, it personalizes send time per subscriber based on when they individually engage.
