Confidence Interval
CI = estimate ± (z-score × standard error). Use this calculator to compute the basic CI as a percentage.
Standard 95% CI uses z = 1.96. Width depends on sample size and variability.
Worked examples
Mean 50, SE 5: 95% CI = 50 ± 9.8 = 40.2 to 59.8.
Frequently asked questions
Why 1.96?
It's the z-score for 95% confidence in a normal distribution.