A/B test duration calculator
An A/B test's duration is the traffic it needs divided by the daily visitors entering it. Enter your visitors, your conversion rate and the lift you are after, and the calculator tells you how many days it takes, rounded to whole weeks.
By Fernando Blanco Dosil · Updated November 2, 2026
Work out your test
For example, 3 if 3% of visits convert
Relative: 20 means going from 3% to 3.6%
- Visitors per version
- 13,914
- Recommended duration
- 4 weeks
- Visitors in total
- 27,828
- Days of traffic needed
- 28 days
Why whole weeks
A Monday does not buy like a Saturday. If you stop a test mid-week, one version can come out ahead just because it got more good days. That is why we always round to whole weeks and never recommend less than seven days, even when the traffic would allow it.
What to do if it comes out too long
More than six to eight weeks is usually a bad sign: in that time campaigns, the season and even your catalogue change. You have three ways out.
- Test a bigger change, one that could move conversion by more than 20%.
- Measure a more frequent conversion: add to cart or checkout start instead of purchase.
- Drop variants. Each extra version splits the same traffic into more groups and, with more comparisons against the original, each group also needs a bigger sample.
How Bixlow does it
In Bixlow every test has a minimum sample and a minimum duration. Even if a variant is ahead on day one, no winner is named until both are met and the probability of being best reaches 95%. Until then, the panel tells you what is missing.