The 15 Most Powerful Words in Subject Lines


The inbox can be a hostile place. With a million 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 the 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
(what’s this?)
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:

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.

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