A/B Testing

Put your subject lines to the test.

Maximize your email open rates with subject line A/B testing.

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How to run an email subject line test.

A-B Testing

Create two options

Create an email with two subject lines.

Send email

Send to contacts

Send the test to a portion of your contact list.


Test picks best line

We automatically send the winner to your remaining audience.

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Increase your open rates. Improve your email campaigns.

Email marketing experts agree: Running an A/B test on subject lines maximizes your email open rates. It's a best practice used across the industry, and Constant Contact makes it easy to implement in your email campaigns. Our tool tests two subject lines on a percentage of your target audience, then automatically sends the winner to the remainder of your contact list.

The best subject line. Every time.

With subject line A/B testing, confidence comes easy. Turn any email campaign into an A/B test to make sure you're sending a subject line proven to generate more opens and increase customer engagement.

Use our best-in-class editor to create an email for testing. Simply start a new email from the campaign picker, then select Subject Line A/B test.

Select the percentage of your contact list that will receive each subject line. To achieve statistical significance, we recommend testing each line on at least 1,000 contacts, if possible.

Choose how long to wait—6, 12, 24, or 48 hours—before declaring a winner. The tool selects the best subject line based on the number of opens, and automatically sends it to your remaining audience.

While the test is active, access real-time reporting to view engagement for each audience and which line is in the lead. Then see how the winning subject line performed overall.

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Resource Center

Resources to help you do more business.

How to Write a Great Subject Line

A subject line is the first impression you’ll make on your readers. Make it count.

11 Surefire Subject Line Secrets

Here’s one: The most effective subject lines contain around 4-7 words or 40 characters.

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