Sample Size Calculator — Two Proportions

How many subjects per group to detect a difference between two proportions, with dropout adjustment and subgroup warnings.

Baseline rate p₁

Target rate p₂

Significance level α (two-sided)

Power (1 − β)

Expected dropout / non-response

I plan subgroup analyses (e.g. by region or segment)

Calculating…

Required sample size per group across a range of target rates. The marker shows your current inputs — smaller effects explode the required n.

Assumption check

Compares two independent proportions (conversion rates, response rates, defect rates). Two-sided test, equal group sizes, normal approximation.

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