Published by Gbaf News
Posted on October 4, 2017
5 min readLast updated: January 21, 2026
Study of more than 30,000 email subject lines finds no correlation between subject line length and performance
Marketers need to abandon the false belief that less is always more when it comes to email subject lines, according to a study by Persado. In a study of more than 30,000 subject lines from Persado’s content database across four key sectors including financial and insurance services, there was no perceptible correlation between performance for opening and click-through rates and subject length. At the same time, a belief that subject length is one of the primary reasons for email success is steering marketers away from delivering content that has personal and emotional relevance to the character and inspire action.
“’Best practices’ are often anything but – this analysis debunks the prevailing, unsubstantiated belief that shorter subject lines are better,” said Assaf Baciu, Co-Founder and SVP of product at Persado. “If anything, in many instances, longer subject lines showed a marginally improved response from consumers. While a shorter headline might be a result of using simple, clear language, it should never be an end in itself. Instead, marketers should use language that provokes the right emotional reaction, whether that takes five words or fifteen. Unless they can adapt to this, marketers will continue wasting their time fine-tuning subject lines that have precisely zero effect on engagement.”
Persado examined more than 30,000 subject lines from its cognitive content database, a constantly growing collection of over one million tagged words, phrases, and images continuously scored against marketing performance. The test was implemented across four groups, based on subject length frequencies: 9-50 characters, 51-61 characters, 62-75 characters, and 76-197 characters. The data was also evaluated across the retail & e-commerce, financial & insurance services, telecommunications, and travel & hospitality industry verticals. In every case, the analysis showed very weak or no correlation between response rates and the length of e-mail subject line.
“Subject line length is only one example of so-called received wisdom that leads marketers down the wrong path,” continued Assaf Baciu. “Practices such as using puns to add character for specific seasons and events; and scrupulously avoiding using emoji are all seen as best practice for subject lines, but amount to being tone deaf to what consumers might want, and actively harm their message’s performance. True engagement is achieved when marketers tailor messages to their own audience and their preferences, not by blanket best practices. Putting too much credence in marketing myths around subject line length drives marketers further away from sparking the emotional connection that really works with customers.”
Study of more than 30,000 email subject lines finds no correlation between subject line length and performance
Marketers need to abandon the false belief that less is always more when it comes to email subject lines, according to a study by Persado. In a study of more than 30,000 subject lines from Persado’s content database across four key sectors including financial and insurance services, there was no perceptible correlation between performance for opening and click-through rates and subject length. At the same time, a belief that subject length is one of the primary reasons for email success is steering marketers away from delivering content that has personal and emotional relevance to the character and inspire action.
“’Best practices’ are often anything but – this analysis debunks the prevailing, unsubstantiated belief that shorter subject lines are better,” said Assaf Baciu, Co-Founder and SVP of product at Persado. “If anything, in many instances, longer subject lines showed a marginally improved response from consumers. While a shorter headline might be a result of using simple, clear language, it should never be an end in itself. Instead, marketers should use language that provokes the right emotional reaction, whether that takes five words or fifteen. Unless they can adapt to this, marketers will continue wasting their time fine-tuning subject lines that have precisely zero effect on engagement.”
Persado examined more than 30,000 subject lines from its cognitive content database, a constantly growing collection of over one million tagged words, phrases, and images continuously scored against marketing performance. The test was implemented across four groups, based on subject length frequencies: 9-50 characters, 51-61 characters, 62-75 characters, and 76-197 characters. The data was also evaluated across the retail & e-commerce, financial & insurance services, telecommunications, and travel & hospitality industry verticals. In every case, the analysis showed very weak or no correlation between response rates and the length of e-mail subject line.
“Subject line length is only one example of so-called received wisdom that leads marketers down the wrong path,” continued Assaf Baciu. “Practices such as using puns to add character for specific seasons and events; and scrupulously avoiding using emoji are all seen as best practice for subject lines, but amount to being tone deaf to what consumers might want, and actively harm their message’s performance. True engagement is achieved when marketers tailor messages to their own audience and their preferences, not by blanket best practices. Putting too much credence in marketing myths around subject line length drives marketers further away from sparking the emotional connection that really works with customers.”
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