The inbox is a hostile place. With a squillion other emails jostling for your subscribers’ limited attention, it’s important that you make your subject line stand out – and get your email opened.

So, what works best? We pored through thousands of campaigns to shortlist 15 popular words – and find out what makes an effective subject line.

While we’d love to say that we’ve found the “silver bullet” to getting people to open your email, our research indicates that, so far, there is no magical formula or golden combination of words that can guarantee an open. Sorry, everyone. What works best for a particular piece of content in one industry, does not ensure the same responses with another.

But, if you look at the data, there are certain patterns that emerge. So we can certainly provide pointers on how certain words perform, as well as practical tips for writing subject lines.

Finding our “Power Words”

In our initial study on subject line performance, we decided to look at how specific words influenced the open rates of campaigns overall. We realized that in order to really understand performance of certain words, we needed both a control group and a test group for comparison – being campaigns with words we had narrowed down for analysis. Both the control and our test group made use of the same lists (minimum of 500 subscribers) between January 1, 2013 until March 31, 2014. In order have enough data to be significant, the list had to be sent at least 10 campaigns over that period – this resulted in a sample of 3,941,735,015 recipients (!!), from 360,872 campaigns and 11,207 lists.

From this modest sample, we narrowed down the most frequently used words that featured at the beginning and end of subject lines, then compared the open rates between our two groups to determine which words performed better, that is, increased the chance of an email being opened. It’s cheesy, but we’ll call these high-performers our “Power Words”.

So, what makes a “Power Word”?

First, some quick notes about our word shortlist. While some words boosted a subject line’s success when they featured as either the first or last word (eg. “Invitation”, or dates), others only provided a notable open % uplift at one end or the other of a subject line. This is in part due to grammatical correctness – for example, a pronoun like “We” or present participle like “Introducing” would seldom feature at the end of a sentence.

Personally, I think it’s important to make these distinctions if only to highlight that word order (and context) matters. As much as it would be lovely to string words together and see your open rates go up exponentially, there are no shortcuts to the ideal subject line.

We’ll share with you some of our other observations and advice, but let’s get into “Power Words” already:

First word: Open % Change Last word: Open % Change
[firstname,fallback=customer],
(what’s this?)
14.68%
Invitation 9.45% 7.69%
Introducing 7.36%
We 5.87%
A 4.09%
Your / You / You! 4.07% 6.20%
Year, eg. 2014 3.89% 2.84%
Update 3.69%
New 3.26%
Month name, eg. June 3.25% 3.34%
Special / Specials 2.75% 2.08%
News 1.31% 2.22%
Sale / Sale! 2.40%
Events 1.97%
Offer / Offers 1.86%

How can I improve my subject lines?

There are a few trends that can be found by looking at our Power Words. These include:

  • Personalization rules – It’s said that a person’s favorite word is their own name and now, we have the facts to back this up. Without a doubt, subject lines that are personally addressed, do the best – just don’t forget to test! Here’s more on subject line personalization.
  • Personal pronouns work, too – Don’t have your subscribers’ names handy? The popularity of “We” and “You/Your” shows that subject lines that make some kind of appeal to the reader are more likely to get a response.
  • Make it timely – Another trend to note is that subject lines that feature dates, or urgency seem to perform better than those that don’t. Holding your subscribers to a date to act, or letting them know that you’re waiting on them (with say, “Invitation”) can be a very persuasive tactic.
  • Be exciting! Finally, we noticed while doing this research is that subject lines that end with an exclamation mark tend to result in more opens than those that don’t. While we don’t encourage everyone to go overboard with enthusiastic exclamations (!!), it’s certainly interesting to see how a little extra energy in your subject impacts email behavior.

We hope that this look at “Power Words” in email subject lines was as revealing to you as it was to us. Keeping in mind that the percentage changes noted above can be quite minimal in the grand scheme of things, it’s worth looking at subject line optimization in the bigger picture of open rate -maximizing tactics, including ensuring that you keep a clean, engaged list and well, get into the inbox in the first place.

Finally, we’d love to know what you’ve been learning – have you run an interesting A/B test on subject lines, perhaps even with the above words? We’d love to know what you found out in the comments below.

  • LogicBase Interactive

    Finding the right words is one of the most difficult thing to think of. Thanks for sharing some of you testing, this is one BIG help!

  • Simon Garlick

    On the subject of exclamation marks:

    The default Spamassassin rules PLING (subject contains a ! character) and PLING_PLING (subject contains multiple ! characters) boost a message’s Spamassassin score by 0.8 and 1.2 respectively; a vanilla Spamassassin installation blocks messages once they hit a score of 5.

    So if you’re sending to a domain that has Spamassassin sniffing headers, the presence of exclamation marks MAY prevent the message from reaching the recipient.

    However my own testing backs up the suggestion in the article: exclamation marks used sensibly in the subject line tend to increase open rate.

    So “being exciting” may mean your message doesn’t make it through, but if the message makes it through then “being exciting” tends to get the message opened by those people who DID get it.
    So

  • Steven Klukowski

    Nielsen Norman Group had a recent article on this same subject:

    https://www.nngroup.com/articles/email-subject-lines/

    Interestingly, they recommend against personalizing the subject line.

  • Ravi

    Agreed, the inevitable need of the hour ! Getting the words right for subject lines is indeed a herculean task for marketers. Thank you for sharing the results of your test!

    We at email monks believe that an email subject line must contain a glimpse of what is inside the email which provides the reader a reason to open the mail. Subject lines must be effective enough to tell and sell what’s in the email.

  • Ros Hodgekiss

    That’s a very interesting counter-point Steven – thank you for sharing! I can understand the rationale behind explaining the email’s actual content early in the subject line, but would be curious to see the data to back up this assertion. The Nielsen Norman Group are a fantastic source of information, so I’m sure their methodology makes a great read in its own right :D

  • Claire Greenhow

    Looking for inspiration for a charity email subject line, you’ve given me a few ideas.

  • Susan Walsh

    Thanks for all the great ideas Ros – I never know if it’s spammy to have the word “sale” in an email so I usually use “special offer”.

  • Kim

    Is there an updated version of this for 2016?

  • Kim

    Hi Kim,
    We recently wrote this post that has over 80 marketing words to help improve your email campaigns that I think you’ll find helpful.

    Cheers and thanks for reading,
    Kim S.

  • Kim

    This post is dated 2014. Is there anything recent?

  • Kim

    Hi Kim,
    This 80+ marketing words post is from Feb. 206. I think you’ll find it helpful.

    Cheers,
    Kim

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