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Confidence Interval Calculator

Estimate a population value from your sample, and show how uncertain that estimate is. Choose what you want an interval for, enter your summary statistics, and the calculator gives the interval with its standard error, critical value and the working behind it.

Free, no account

The calculator chooses the method for each.

The mean of one sample, such as average test scores.

Your sample

For example, 72.4.

The standard deviation of your sample (s), not a known population value.

The number of observations, at least 2.

Confidence level

95% is the most common choice.

Choose what you want an interval for, enter the values, and press Calculate.

What should I do next?

You have an interval. Now report it with the effect.

  • Effect Size Calculator

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  • Results Interpretation Assistant

    Explains the statistical results you already have: what they mean, whether they are significant, and how they bear on your hypotheses, objectives and research question.

  • Confidence Intervals

    What a confidence interval is and isn't, how standard errors, critical values and margins of error produce one, how intervals for means, proportions, their differences and correlations are calculated, and how to interpret and report them.

How to use it

  • Choose what you want a confidence interval for: a mean, a difference between means, a proportion, a difference between proportions, or a correlation. The calculator chooses the method.
  • Enter the summary statistics from your sample, and choose the confidence level, usually 95%.
  • Read the interval with its estimate: the estimate is the single best guess, and the interval shows the range of population values the data are compatible with.
  • Report the estimate, the confidence level and the interval together, and describe how the data were collected.

What it doesn't cover

  • Regression coefficients, odds ratios, risk ratios, hazard ratios, ANOVA contrasts, medians, and Spearman or other non-Pearson correlations.
  • Bootstrap intervals, Bayesian credible intervals, prediction intervals and tolerance intervals: they answer different questions.
  • Intervals from raw data: enter summary statistics, such as a mean, standard deviation and sample size.
  • Whether your data meet the method's assumptions, or whether the sample represents the population you want to describe.

Privacy

Calculations run entirely in your browser. The values you enter are not sent to ResearchKit or anyone else, and they aren't stored.