Free online Confidence Interval Calculator. Enter sample mean, standard deviation, and sample size to calculate 95% and 99% confidence intervals. Perfect for AB testing, research, and statistical analysis. Pure frontend, private & secure. | No sign-up · Data never uploaded
Zero Dependencies · Works OfflineA confidence interval is a statistical range that likely contains the true population parameter (e.g., population mean). A 95% CI means: if you repeated sampling 100 times, about 95 of the calculated intervals would contain the true population mean.
CI = Sample Mean ± Z × (SD / √n). Z-values: 90%→1.645, 95%→1.96, 99%→2.576.
AB test result evaluation, survey data analysis, quality control sampling, medical research statistics, market research error estimation, and more.
95% is the most common confidence level in academic research and business analysis. It means there's a 95% probability the true value falls within the interval.
Generally n≥30 is recommended. Larger samples produce smaller standard errors and narrower CIs. For small samples (n<30), consider using t-distribution instead of normal distribution.
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