11 Subject Line Formulas That Boost Open Rates

Hey, it's Raymond here. Welcome to the first issue of our newsletter!

I’ve been in the e-commerce space for 7 years now, and one of the first and very important things I’ve learned: 

The subject line can make or break your open rates.

When I first got started, I was overwhelmed by how competitive the inbox could be. 

With an average office worker receiving 121 emails a day, I had to figure out how to stand out, fast. 

And trust me, it didn’t happen overnight. 

But after years of testing, tweaking, and analyzing,  I cracked the code. 

And now, I’m about to share the formula with you.

Here’s the deal: The subject line is your first and best chance to grab attention. 

It’s not about being clever—it’s about being effective.

So, what’s the secret? 

Let’s dive into the 11 formulas I wish I knew when I started.

And don’t forget, this is a two-way street. 

Reply to this email and drop your thoughts. 

Let’s make this a conversation.

Formula #1: Keep Your Subject Line Length Between 41 and 70 Characters.

Here’s a tip I wish I had known earlier: Your subject line needs to fit perfectly on your reader’s screen. 

I’ve seen too many subject lines get cut off because they were too long. 

When I started optimizing for mobile, I realized most of my audience uses iPhones and Gmail. 

Did you know that iPhones display about 41 characters, and Gmail allows up to 70 characters?

Therefore, keep it short and sweet within this range—anything longer risks being cut off.

Here are a few examples that really work:
"Exclusive Deals Just for You–Don’t Miss Out!" (44 characters)

"Get Ready for the Ultimate Shopping Experience" (46 characters

Example:

Formula #2 Short and sweet is the way to go—why your subject line should never exceed 9 words.

I learned early on that people don’t read—they scan. 

So, if your subject line goes over 9 words, it gets harder to process. 

Studies even show that our brains can process shorter phrases more quickly. 

That’s why I started testing with just 9 words or less—and the results were significant.

Example:
"Boost Your Email Open Rates—Here’s How" (7 words)
"Exclusive Discounts Just for You" (5 words)

Formula #3: Always lead with the most important words—make sure your message hits the mark from the start.

If your subject line gets cut off, you need the important part at the start. 

Don’t bury the lead. 

Make sure the core message hits them right away.

Here are some great examples of do’s and don’ts:
🚫 “You’re Missing Out on This Huge Discount”
✅ “Huge Discount Inside – 24 Hours Only”

Formula #4: Numbers and power words work wonders—use them to grab attention.

Let’s face it—numbers stand out. 

Whether it’s a list or a percentage, numbers are easier to digest and get attention. 

I’ve been using them for years, and they’ve made a huge difference.

Example:
🚫 “Check Out Our Latest Blog Post”
✅ “5 Marketing Hacks You Need Today”

Formula #5: Stack the benefits to make your subject line unstoppable.

This one is a game-changer. 

When your email offers multiple benefits, combine them in one line. 

After testing for years, I’ve found that when I stack two benefits together, the reader’s curiosity spikes!

Example:
"Boost Open Rates and Increase Clicks—Here’s How"

Formula #6: Tease your readers with a mystery they can’t resist—the power of the curiosity Gap.

When I use this, my readers often feel like they have to open the email.

Tease your reader with a mystery or an unexpected twist. 

This is one of my favorite formulas because it taps into the human need to know more. 

Example:
"You’re Probably Making This Costly Email Mistake"

Formula #7: Personalization works like magic—why using names in subject lines can boost open rates.

Personalization works wonders. 

If I use someone’s first name in the subject line, I’ve noticed my open rates improved. 

It’s as simple as that. 

People like to feel like they’re special, and using their name can work wonders.

For example:
“Hey Anna, Here’s Your Exclusive Offer”

Formula #8: Make your readers feel the urgency—how to use scarcity to drive action.

We all know FOMO (fear of missing out) drives action. 

When there’s a limited-time offer or exclusive deal, make sure to highlight that urgency. 

I’ve usually used this formula for time-sensitive promotions.

Example:
“Only 3 Spots Left – Book Now!”

Formula #9: Ask questions that spark curiosity—engage your audience with a thought-provoking query.

Questions spark curiosity. 

They draw people in and get them thinking.

If the question is timely and speaks to something they care about, they’ll be way more likely to open your email.

Example:
"Are You Making This Email Marketing Mistake?"

Formula #10: Reverse psychology can be a powerful tool—use humor and contradiction to get attention.

This formula works best for educational content. 

It uses humor and is a bit cheeky, but trust me, it gets attention. 

For example:
“How to Lose Customers Fast (A Complete Guide)”

Formula #11: Make your readers feel like VIPs—why exclusive insider information gets so much attention.

People love feeling like they’re getting VIP access, and it can really make an impact.

Who doesn’t want to feel important, right?

This works especially well when you're launching something new or sharing behind-the-scenes glimpses.

Example:
“A Sneak Peek at Our Newest Feature”

What’s Next?

So, now that you’ve got the formula, it’s time to A/B test at least two subject lines in your next campaign. 

This is the best way to figure out which one resonates with your audience.

To back this up, here are some data that will show how important subject lines are:

At the end of the day, email marketing isn’t just about hitting send—it’s about creating real connections with your audience. 

When done right, it’s hands-down one of the most profitable channels you can have. 

But if you’re feeling stuck or not seeing the results you were hoping for, don’t stress.

That’s exactly what I’m here for.

Let’s turn those challenges into opportunities.

Talk soon,
Raymond Chen
Founder & CEO, 11 Agency

Let’s Make This Work for You

There’s a lot that goes into building a high-converting email strategy. 

If you’re serious about optimizing your email marketing, let’s talk. 

Here’s what we can do:

✅ Done-for-You Email Strategy: If you’re ready to scale but don’t have the time, we’ll build out a full email system that maximizes your revenue. You can book a call with me here. 

✅ Or, if you just want to grab a free resource, get a FREE 10-page KPI audit and a 128-point health scorecard to optimize your email marketing. Get it here!

More Resources to Help You Win at Email Marketing

If you’re up about boosting your email game, I’ve got a few more gems for you:

📝 Read Our Latest Blog
Want more subject line insights? Our head copywriter, Lawrence Soliman, just dropped an in-depth guide on crafting the perfect Thank You email subject line—with examples you can swipe today. Don’t miss it.

💡 Let’s Connect on LinkedIn
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