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📉 Confidence Interval Calculator

Build confidence intervals for means, proportions, and differences between groups at 80%, 90%, 95%, or 99% confidence levels.

Confidence Interval Calculator

Build confidence intervals for means, proportions, and differences between groups. Choose a confidence level (80%, 90%, 95%, or 99%) and see the center, margin of error, and interval endpoints.

Interval type

Confidence interval for a single mean using z* s / √n.

Inputs

Confidence level

Critical value method

Sample mean (x̄)

Sample standard deviation (s)

Sample size (n)

confidence interval calculator95% confidence interval for mean or proportion

Interval summary

Critical value (z* / t*)

1.96

Degrees of freedom (t)

Point estimate

Margin of error

0.715691

Confidence interval

(9.284309, 10.715691)

How to use this tool

Choose the type of confidence interval you want to build (mean, proportion, or difference).
Enter the relevant sample statistics and select a confidence level such as 95%.
Read off the point estimate, margin of error, and the lower and upper bounds.

Confidence interval calculator for exams

Quickly check 95% confidence intervals for means and proportions against your working.
Experiment with different confidence levels to see how the margin of error changes.
Use the difference in means or proportions to compare two groups with a single interval.

What this CI calculator assumes

Uses z critical values by default, with optional t critical values for small-sample mean intervals.
Assumes reasonably large samples or approximate normality so normal and t approximations are valid.
Intervals are two‑sided and symmetric around the point estimate.

FAQ

Does this use z or t for the confidence interval?: You can choose. For large samples, use z. For small samples when estimating a mean, switch to t and the calculator will use an approximate t critical value based on the degrees of freedom.
Can I enter percentages instead of proportions?: Enter proportions as decimals between 0 and 1 (for example, 0.4 instead of 40%). This keeps the formulas consistent and reduces confusion.
What does a 95% confidence interval mean in plain language?: Roughly speaking, if you repeated the sampling process many times, about 95% of the constructed intervals would contain the true parameter.

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