4 Cold Email Subject Line Formulas That Work [+Examples!]

Contrary to what we’ve all been taught, people are still very likely to judge a book by its cover, especially when it comes to cold emails.

A single phrase — your email subject line — can either make or break the whole sequence.

Failure to grab the reader’s attention or stand out in some way will have most recipients simply deleting the email without giving it a second thought, regardless of how meaningful your message is. Worst case scenario? They’ll also report your email as spam.

Making a good first impression with your subject line, on the other hand, can help you start a conversation and open unlimited business possibilities.

That is why I’ve decided to share some of the best practices on how to write a great subject line for email we’ve developed over the years along with the proven formulas and templates to spur your imagination.

Effective subject lines: the dos and don’ts

On the topic of crafting a perfect subject line, there are tons of tips and tricks to increase your open rate. Just google it and you will find dozens of guides and resources claiming to have cracked the code for the perfect cold email subject line.

Yet, in my opinion, people tend to overcomplicate (or even overhype) this topic. 

Working in the industry for over 5 years, I’ve tried every cold emailing trick in the book. But in reality, all good subject lines for cold emails boil down to the following rules:

• Keep it as short as possible
  I recommend using subject lines that consist of 3-5 words max. And that is not only because intricate and lengthy subject lines are harder to comprehend. 
  Most popular desktop email clients will show only about 60 characters while on mobile devices your subject lines will be cropped to just 25 to 30 characters. So be concise if you don’t want half of your subject line to get cut off.
• Communicate the main idea of your email
  A short subject line doesn’t mean it can’t be informative and engaging. Try to make the reason for your outreach clear right away. This is a good way to show your prospects that you value their time as well as avoid getting reported for spam. At the same time, you shouldn’t give away too much information in your subject line — your goal is still to make the prospects open the email and learn more.
• Make it feel personal
  One of the keys to effective cold outreach is to make it feel like each of your emails has been sent manually to each individual prospect. And the subject line is no exception to this rule. A good idea would be to add a prospect’s name or mention their company. It’s even better that you can do this at scale by simply adding variables to your subject lines (you will see a ton of those in the examples below).

Pro tip: While it is generally believed that using numbers or emojis in your subject lines can boost your open rate, I wouldn’t say either type is a must-have. Such tactics might work for some audience segments or serve a specific purpose. Still, it’s best to A/B test such subject line variants first so you can be sure they work in your particular case. Consider using an AI writing assistant to help you do as much A/B testing as possible so you’ll have more data to work with.

If the listed tactics are generally considered to be the best practices to follow in your subject lines, it’s only natural that there are also some mistakes you should avoid. And I’m not talking about the obvious no-noes like writing your subject line in all caps. 

Some of the common outreach blunders are:

• marketing talk, i.e., presumptuous statements about “the best” or “industry-leading” product/service — you aren’t a marketing manager and your email is not a newsletter.
• tricky subject lines, including the ones starting with “Fwd:” and “Re:” — your goal isn’t just to get more opens, but to build relationships (which is impossible to do using deceit).
• spam words — these might sound OK to a person but will definitely get your emails noticed by spam filters hurting your deliverability and sender reputation (you can find some examples of such words here).

The proven email subject line formulas

Considering the listed dos and don’ts, I have identified 4 subject line formulas that constantly generate high open rates:

• mutual business formula,
• 3-variables formula,
• need/urgency formula, and
• personalization formula.

Let’s take a closer look at each one of these formulas that will help you come up with good subject lines for cold emails (including ready-to-use examples).

The mutual business formula

As mentioned above, tricking the prospects into opening your emails can only get you so far. 

That’s why I try to make my outreach emails as straightforward as possible — I’d rather have a lower open rate than annoy my prospects with vague subject lines.

And what I like to call the “mutual business” subject line formula is a perfect way to convey your message in a clear and concise manner.

Here are some variations of good subject lines for emails using this formula:

• {{Company}} <> {{My Company}} — Google <> Reply.io

• {{Company}} and {{My Company}} — Google and Reply.io

• {{Company}} <-> {{My Company}} — Google <-> Reply.io

• {{FirstName}} and {{My FirstName}} — John and William

• {{My Company}} for {{Company}} — Reply for Google?

The 3-variables formula

The subject lines that follow the so-called “3-variables” formula use a similar approach. These typically contain 3 words, i.e., variables, that might not even be logically connected (at least at first glance). 

As a result, the formula breeds success if you’re looking to arouse the prospect’s curiosity about what’s behind the subject line. Yet, be careful: Be sure there’s a clear link between the subject line and the email content to avoid coming off as deceitful.

Here are some of my favorite variations of this formula:

• {{Interest}}, {{Company}} and {{My Company}} — Marvel, Google and Reply.io (if the prospect loves watching Marvel movies)

• {{Company}}, {{My Company}} and {{Technographocs}} — Google, Reply.io and Salesforce (if the prospect company uses Salesforce)

• {{Company}}, {{My Company}} and {{Pain Point}} — Google, Reply.io and sales automation

• {{Quarter and Year}}, {{Interest}} and {{Company}} — Q1 2024, golf and Google

• {{Quarter  and Year}}, {{Company}} and {{Pain Point}} — Q1 2024, Google and sales automation
• {{Hirings}}, {{Company}} and {{Pain Point}} — 2 new SDRs, Google and sales automation

The need/urgency formula

Creating urgency is one of the common closing techniques used by sales professionals to move deals further through the sales pipeline. 

This tactic can be applied in cold outreach as well. For example, the subject lines that ask a question, address a need, or mention a time-sensitive matter can help you generate curiosity and urge the prospects to open your emails.

Here are some examples of the formula we use at Reply:

• {{FirstName}} – any thoughts? — John – any thoughts?

• {{FirstName}}, just curious… — John, just curious…

• {{My Company}} trial account ends in 2 days — Reply trial account ends in 2 days

• Have you given up on {{Pain Point}}? — Have you given up on sales automation?

The personalization formula

The above-listed formulas fit perfectly with automated sales outreach. You can add as many variables as you need to both your subject line and email template and still put the whole process on autopilot using a sales engagement platform like Reply.

The personalization formula, on the other hand, is something I prefer using for one-on-one email communication and manual emails in the sequence so I can still automate subject lines but not the whole outreach (e.g., when adding a custom snippet or Vidyard video).

Here are a few good email subject lines using this approach that worked for us:

• I made you a video, {{FirstName}} — I made you a video, John

• {{FirstName}} + {{My FirstName}} = intro video — John + William = intro video

• {{FirstName}}, here’s something just for you — John, here’s something just for you.
• {{FirstName}}, {{Colleague}} > referral — John, Max > referral

Decoding the “perfect” cold email subject line

You can follow all the best practices and proven tactics on how to write a good subject line for email marketing. Sadly, none of them can guarantee the results you expect. The only way to understand if your subject line is any good is to try it in practice (or run an A/B test with several options) and watch your open rate.

To help you make sense of the metrics and evaluate the effectiveness of your subject lines, here are some benchmarks to give you an idea of what you should be looking for.

1. A good subject line is the one that generates at least a 30-40% open rate. 
2. A great subject line typically drives up to a 40-50% open rate.
3. A perfect subject line will consistently show an over 50% open rate.

For the past 6 years, I’ve tested out dozens of subject lines using different formulas. But there’s one subject line that works EVERY TIME, consistently generating a 50%+ open rate across all prospect segments (Tier 1, Tier 2, and Tier 3 accounts). And it doesn’t matter whether it’s a decision-maker, an influencer, or an evaluator! 

Sometimes, we even get an 85%+ open rate with the given subject line — mostly for the laser-focused lists.

The subject line is:

{{Company Name}} <> {{My Company}}

In our case, it’s “{{Company Name}} <> Reply.io”

Yes, it’s that simple! So what makes this no-brainer subject line so effective? 

First of all, it clearly ticks all the boxes for the rules I mentioned above and follows my mutual business formula. 

Other ingredients in this success sauce, in my opinion, are:

• We put the prospect’s Company Name first because it’s all about them, not us.
• We use the “ <> “ symbol to indicate an opportunity for mutual business, partnership, relationship, or synergy — call it whatever you want.
• We are not trying to trick anyone, clearly stating our company name. So, if they already know about us, this might give them another reason to open the email.

Conclusion

The first impression is indeed the most lasting — especially in cold outreach! So, don’t underestimate the importance of subject lines when planning your sequences. 

My hope is that the listed formulas will give you an idea of what an effective subject line might look like. Just don’t blindly copy the examples I’ve provided! Try to find your unique voice and approach to your target audience — experiment and see what works for you.