You put a lot of effort and time into creating the perfect email content for your subscribers. But no matter what you write, or how well, people may not even see your email if the subject line doesn't get them to click on your email.

In a world full of distractions, it's hard to get and hold the attention of your email subscribers. That's why I've outlined 10 subject line formulas proven to get subscribers to open emails.

1. The Social Proof Subject Line

Social proof is a powerful driver of human behavior and affects many of the decisions we make. For example, people generally won't buy a product from a site until it has reviews and ratings.

Social proof is a powerful marketing tool because it shapes consumer perception and brand reputation. Also, it shapes how we think about a certain business, product, or services.

There are various ways to leverage social proof to make your subject lines more compelling. For example:

• The advertising formula Mark Cuban used to make his fortune
• How Airbnb become a $30 billion company
• Why 2,632 of our clients would recommend our business coaching services to a friend

2. The Data Subject Line

Another powerful email formula is to include data, numbers, or statistics in your subject line.

If you share factual information backed with truthful data and numbers, you will get a better open rate with your emails.

Including data in your subject line will not only increase your credibility but also build rapport as a brand that provides reliable information and solutions.

Let's see some examples:

• Blog content with an image gets 120% more engagement
• How to increase customer value by up to 600%
• Little known SEO tactic increased my leads 132%

3. The Curiosity-Gap Subject Line

Upworthy and Buzzfeed have built their content empire around piquing their audience's curiosity. In his seminal paper titled The Psychology of Curiosity: A Review and Reinterpretation, researcher George Loewenstein called this psychological phenomenon "the curiosity gap."

The curiosity gap describes the curiosity that arises when there is a gap in our knowledge that we're curious to fill. You can create an overwhelming sense of curiosity in your audience if you leverage this powerful approach in your email subject lines. (But your subscribers don't like to be deceived or cheated, so make sure your emails deliver the promise in the subject line.)

Here are some examples:

• What Lady Gaga can teach about content marketing
• We were surprised by how well this one tactic worked
• I lied to you about...

4. The Surprise Subject Line

The emotion of surprise is addictive and influential, and it triggers positive feelings like importance and self-worth.

Whether the surprise is a small piece of content or an expected free offer that benefits users, it moves the reader to open your email and learn more.

Some examples:

• I've got a gift for you!
• When "less is more" is bad advice
• When "more is better" is bad advice

5. The Announcement Subject Line

Announcing something new in your subject line is a great formula to make your subscribers open your emails.

If you have something new to announce to your list, state it directly and clearly, without using copywriting tricks or trying to be smart. For example:

• See our new blog templates
• Latest update to your software is here
• Introducing Sendlane: a better way to send emails.

Words like "new" and "update," and "introducing" let your subscribers know that something new has come up that they don't know about yet, encouraging them to open your emails.

6. The Scarcity Subject Line

It's not surprising that scarcity marketing works. Scarcity is a powerful human driver and people always want something that is rare or difficult to get. As the law of supply and demand states, low supply of a product and high demand for it will typically increase its value.

When you add limited availability and a time limitation in your email subject, the fear of missing out kicks in and compels the readers to act before it's too late:

• You've got ONE DAY to get this
• Hurry! Only 3 consultation spots left
• Last chance to get 30% off

For you to leverage the power of this email formula, your readers have to be engaged with your content and the scarcity must be genuine.

So make sure the content or offer you're presenting is important to your readers before you bring scarcity into it to push them to act quickly.

7. The Personalized Subject Line

When you include your subscriber's name into the subject line, it feels more like a message that's written specifically for each recipient.

You can combine personalized emails with other formulas for maximum impact:

• John, 8 out of 10 content marketer are doing SEO wrong
• John, this is embarrassing but...
• TWO HOURS LEFT, John: It's your Last Chance to join my event

8. The Question Subject Line

Questions that prime our curiosity have an incredible power to attract our attention and influence our brain. When you use a question in your subject lines, it will intrigue your readers and inspire them to open your email in search of an answer.

The questions you ask should focus on your reader's specific needs, interests, and curiosity.

By asking a question, you will be able to capture their attention and convince them to open your email.

9. The 'How to' Subject Line

The how-to subject line is a classic. It's deceivingly simple and works extremely well. Your audience wants to solve a problem and is digging through the Internet to find answers.

The formula works because it describes the content of the email in simple and clear language; it also positions you as an expert on the topic, increasing your credibility.

• How to increase your content's exposure
• How to shed belly fat
• How to write sales copy

To maximize this formula's effectiveness, focus on the benefits and the end results.

10. The Numbered-List Subject Line

Numbered lists are common in blog post titles, and they can be effective in email subject lines, too. People like list articles because they're easily consumable and tell the readers exactly what to expect, pushing them to open your emails.

Here are some examples:

• 10 steps to create your first info product
• 30 explosive ways to promote your content
• 5 key aspects of a high-converting landing page

The key to success with this formula is the number you use and how specific you are. Also, make sure your content is not boring or overwhelming.

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No matter how great your email campaigns might be, they're all but pointless if you can't get people to open your emails.

Now that you have the most proven subject line formulas, start testing them to see which work best for getting your subscribers to open your emails.