A/B Test Duration Calculator
How long do you need to run your test before you can make a decision? Stop guessing. Get the exact number of days — before you start.
Results will appear here after you click Calculate.
The #1 reason A/B tests give wrong answers
Stopping a test too early is the most common — and costly — mistake in A/B testing. It creates a 25–30% false positive rate even at "95% confidence." This is called the peeking problem.
The fix: decide your test duration before you start, then commit to it. Never stop early because it "looks like" it's winning. This tool tells you exactly how long you need.
Run tests for at least one full business cycle
Even if the math says 10 days, run for at least 2 full weeks. Weekday/weekend traffic behaves differently — running less than 14 days can create seasonal bias that makes results ungeneralizable.
Need help designing your test roadmap?
Our team prioritizes and sequences tests so you always have valid, actionable results — not a backlog of inconclusive tests.