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# A/B test sample size calculator

Enter your baseline rate and minimum detectable effect and get visitors per variant, run-time estimates from daily traffic, and the full formula trace.

Enter a baseline and an effect to size the test.

The plan is a normal approximation of the two-proportion comparison, computed before the test runs. Real tests also lose visitors to mid-experiment filtering, cross-device doubles, and peeking at partial results, and those losses push the honest number up. Sequential and Bayesian designs need different sizing than this fixed-horizon plan, and the tool says so rather than pretending to cover them.
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## More fake data tools

- [Cohort retention analyzer](/data/cohort-retention-analyzer)
- [Bulk test data](/data/test-data)
[All fake data tools](/data)

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