How this works
A higher open rate in a small test doesn't always mean a subject line actually won — with too few sends, differences can easily be random chance. This calculator runs a standard statistical significance test on your two variants.
A/B test significance calculator
Enter sends and opens for both variants — see whether the difference is real or just noise.
Variant A open rate
Variant B open rate
Difference
NoteStatistical significance depends on adequate sample size — with very few sends, this result may not be reliable even if it says 'significant'.
Frequently asked questions
How many sends do I need for a reliable result?
There's no fixed number — it depends on the size of the difference between variants. As a rough guide, tests with fewer than a few hundred sends per variant often can't detect anything but very large differences.
What does '95% confidence' actually mean?
It means that if there were truly no difference between the variants, a gap this large (or larger) would only show up by chance about 5% of the time — not that you're 95% certain which one is better.