Confidence interval calculator

Compute a confidence interval for a sample mean (z-based, large sample) or a sample proportion at 90%, 95% or 99% confidence.

Sample mean (x̄)

Sample standard deviation (s)

Sample size (n)

Confidence level

95% confidence interval

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Lower bound

Upper bound

Margin of error

z* (critical)

Formulas

CI for mean: x̄ ± z* × (s / √n)

CI for proportion: p̂ ± z* × √( p̂ (1 − p̂) / n )

z* values: 1.6449 (90%), 1.9600 (95%), 2.5758 (99%)