The Perfect Subject Line: A Data-Backed Guide

We analyzed 10,000 cold emails to find what actually works in subject lines. Spoiler: everything you've been told about subject lines is probably wrong.

The Data Doesn't Lie

After analyzing 10,000 cold email campaigns across 15 industries, we found patterns that challenge conventional wisdom. Here's what the data actually says.

Finding #1: Shorter Isn't Always Better

The "keep it under 5 words" advice? It's oversimplified. Our data shows:

• 1-3 words: 22% open rate
• 4-7 words: 31% open rate (winner)
• 8-12 words: 28% open rate
• 13+ words: 19% open rate

The sweet spot is 4-7 words — enough to be specific, short enough to be scannable.

Finding #2: Personalization Works (When It's Real)

Subject lines with the prospect's company name had a 41% higher open rate than generic ones. But here's the catch: using just their first name ("Hey Sarah") performed worse than no personalization at all. It feels spammy.

What works: "{Company} + {specific observation}"

Example: "Acme's Q3 hiring push"

Finding #3: Questions Outperform Statements

Questions generated 24% more opens than statements. The brain can't help but try to answer a question when it reads one.

Statement: "Improving your email deliverability" Question: "Is your deliverability costing you deals?"

Finding #4: Lowercase Wins

All-lowercase subject lines outperformed Title Case by 17%. They feel more personal, like a note from a colleague rather than a marketing blast.

Finding #5: Emojis Are Risky

Emojis increased opens for B2C emails by 12%, but decreased opens for B2B emails by 8%. Know your audience.

The Formula

Based on our data, the highest-performing subject line formula is:

{lowercase question} + {company/industry reference} in 4-7 words

Example: "scaling outreach at Acme?"

Simple. Specific. Scannable.