15 Tips and Formulas for Writing Email Subject Lines

Learn how to write effective Email subject lines

Don’t judge a book by its cover, they say. And yet authors pay from $300 to $1,500 for the cover design of a self-published book, according to Reedsy.

Why?

Because first impressions do matter.

And readers do form judgments based on the cover of a book.

In the world of email marketing, the subject line is the reader’s first impression. And, just like book covers, readers judge subject lines all the time.

When the subject line passes judgment, the reader opens the email. When it doesn’t, the reader keeps scrolling.

Great subject lines that stop the scroll and get the open are essential to successful email marketing. So, to be a great email copywriter, you need to master the skill of writing email subject lines.

These tips and formulas will get you started as well as provide inspiration if you ever get stuck for ideas. (You might want to bookmark this page for future reference.)

1. Get the Length Right

An email subject line should be no more than 60 characters… if it’s being viewed on a computer. However, with so much email being read on mobile devices these days — 40–60%, depending on which study you look at — that character count needs to be reduced by about half.

Different devices — and even different settings on the same device — display a different number of characters for email subject lines. So, a good rule of thumb is a 25–35 character range.

Check out this subject line from AWAI. It’s a great example of how much you can convey in a short space.

With that in mind, if your subject line is longer than 30 characters, make sure the most important things are at the beginning and that your subject line still persuades the reader to open the email even if the ending gets truncated.

2. Don’t Capitalize Every Word

A subject line is a sentence, not a title. Only the first word should be capitalized unless it’s a name.

Consider the difference between these similar subject lines:

• Don’t miss out!
• Check These Out

The first — where only the first word is capitalized — is more conversational and feels more personal. The second is more formal and feels more commercial. People are more likely to open the personal email over the commercial one.

3. Choose Your Words Wisely

As writers, we know that words matter. This is especially true in the limited space of an email subject line.

Omnisend has compiled the following list of 70 words and phrases that are proven to see higher open rates:

• Available
• Back in stock
• Better
• Brand new
• Breaking
• Can
• Celebrate
• Contest
• Daily
• Deserve
• Do
• Easiest
• Event
• Exclusive
• Expired
• Expiring
• Fastest
• Find
• Freebie
• Get
• Get this now
• Go
• Great deals
• Hurry
• Important
• Information
• Introducing
• Is coming
• Jokes
• Last chance
• Latest
• Limited time
• Monthly
• New
• News
• Now
• On sale
• Orders
• Plus
• Prettiest
• Promotional
• Really
• Register
• Remember
• Renew
• Review
• Soon
• Special
• Steps
• Still
• Stock
• Tell
• Thanks
• Time
• Today only
• Tomorrow
• Top stories
• Try
• Update
• Upgrade
• Voucher
• Waiting
• Ways
• Weekend
• Weekly
• Wonderful
• Won’t
• Yesterday
• You
• Your

Work these words into your subject lines where relevant and appropriate. Writing with a conversational tone and consistent voice is still more important than using preset words.

4. Use Specific Numbers

Using specific numbers arouses curiosity and adds credibility to an email subject line. Consider these two subject lines:

• NEW: Writing prompts for you
• NEW: 31 writing prompts for you

Many readers will feel curious and want to see what all 31 are. And the number also reassures the reader that reading the email will be worth their time. With 31 writing prompts, they likely feel that they’ll find something they can use.

They may not be so sure with the vague subject line that doesn’t mention a number.

Another note about numbers… The odder the better, typically. (Except for 10… People love lists of 10.) In fact, I’ll bet if you go scan your inbox right now, you’ll find most number subject lines use an odd number like this example from theClikk.

5. Use Active Verbs

Using active verbs in your email subject lines makes them more compelling. For example…

• NEW: 31 writing prompts for you
• Use these 31 writing prompts to write every day (Note: The text in black is 31 characters, so the words in red may be cut off on some devices.)

Other great active verbs for email subject lines are “try,” “do,” and “get.”

Note: Which of these email subject lines is better? Will “NEW” or “Use these” get more opens? We can’t know unless they’re tested against each other. A/B testing — or split testing — in email marketing is the practice of sending two versions of an email with a slight variation of a single element to see which version performs better. 

6. Ask a Question

Using questions in your subject line can increase your engagement. They open a conversation loop that can be closed only if the reader opens the email to find the answer.

In general, you want to keep questions open-ended. It’s best to avoid yes/no questions, because they don’t always get the reader to open the email. For example, the answer to “Filed your taxes yet?” is either yes or no… and neither answer is likely to get that email opened.

There is an exception, though. Questions that have a definite yes or no but also promise a benefit can be effective. For example, “Want to save hundreds on taxes?” That’s technically a yes/no question. But a yes answer is almost guaranteed… and so is the likelihood of the email being opened.

Curiosity questions like this one from Traffic & Conversion are also a strong approach.

I mean, aren’t you just burning to know what Elton John and the Pentagon have in common, never mind what they share with T&C?

7. The “How to [Desired Result]” Formula

Think of “how to” email subject lines as a promise to help the reader achieve something they want. For example, “How to lose 5 pounds this weekend.”

Be careful to make this a realistic promise, though. If it seems too good to be true, readers won’t want to waste their time and won’t open the email… and you may even lose some credibility in their eyes.

8. The “NEW” Formula

An announcement of something “new” is proven to get a reader’s attention and get them to open an email. It could be a new blog post, a new product, a new special offer… For example, “NEW: 10-minute lunch recipes on the blog.”

But “new” must be used sparingly. If you have something new every day or even every week, “new” becomes normal and is no longer special. And when it’s no longer special, it’s easier to ignore.

9. Create a Sense of Urgency

Words like “today only,” “for the next 12 hours,” “last chance,” and “before it’s too late” give a sense of urgency to your email. This type of email subject line gives the reader a reason to open the email now instead of waiting for later, and it’s proven to be very effective.

However, make sure the time deadlines are true. You’ll lose credibility if you say something is available “today only” and then readers can get it tomorrow or next week.

10. Surprise the Reader with Something Completely Unexpected

Studies show that surprise stimulates the brain. So, when you can surprise the reader with something completely unexpected, you get their attention.

For example, “Items left in cart may get trampled by unicorns” or “Biz lessons learned from my dog.” Or this example from Lunchtime Genius…

Just be sure the playfulness matches the brand voice. And, like the “NEW” formula, surprise subject lines should be used sparingly to maintain their effectiveness.

11. The “Better Way” Formula

The promise of a “better way” to do something is nearly irresistible. For example, “A better way to pay employees” or “A better way to grow tomatoes.” These emails are highly likely to get opened.

12. The “Problem with” Formula

Exposing the problem with something is another thing that is hard for people to ignore. For example, “The problem with most dog food” or “The problem with most running shoes.” People want to know what the problem is… and, more importantly, if their fill-in-the-blank thing has that problem.

This subject line from Ed Gandia is a perfect example of this kind of subject line in action…

13. The “Truth About” Formula

Like exposing a problem, revealing the truth about something also tugs at our curiosity. It also appeals to our desire to look smart to others.

Some examples of this are “The truth about flossing” or “The truth about your credit score.” Wouldn’t you like to know these truths?

14. The “Don’t Until” Formula

This formula taps into the fact that we are psychologically wired to want to do something we’re told not to do. Want proof? Don’t eat any chocolate until tomorrow. Give it a minute, and I bet you’ll be craving chocolate!

Adding the “until” takes this desire to do the thing we’re told not to do and gives it a direction. In an email subject line, the “until” is usually directing the reader to “read this” or some variation like it.

For example, “Don’t eat lunch until you read this” or “Don’t go to the beach until you know this.”

A variation on this formula is “Before you [insert action], do this.”

15. Make the Reader Feel Something

Curiosity, fear of missing out, and the desire to get something are all powerful emotions that will get the reader to open an email. Think about what emotion is most appropriate to tap into for your specific email… and then write your subject line accordingly.

Putting It All Together

Consider these top-performing email subject lines shared by AppSumo:

• I was right — and that’s not good for you (69% open rate)
• 13 email marketing trends you must know (64% open rate)
• Before you write another blog post, read this (61% open rate)
• Are we still on for 12? (61% open rate)
• You don’t want FOMO do you? (60% open rate)
• We’re starting in 5 HOURS (59% open rate)
• Missed you, how’s Thursday? (59% open rate)
• How 35 influencers grew their sites from 0-10K visitors (57% open rate)
• It’s time to rethink Black Friday (57% open rate)

Many of these examples combine two or more of our subject line tips and formulas. That’s good. It makes them that much more effective.

Which email subject line tip, formula, or combination thereof will work the best for your client and your situation? You don’t know until you test it. So, give it your best educated guess — or your best two or three educated guesses — and go for it.

Keep track of the results and try to get even better results with the next email.

That’s part of the fun of email marketing. You can always challenge yourself to do better than your previous best. And the more email subject lines you write, the better you’ll get

Thanks to Michele Peterson from AWAI.