Quick start
- Choose Mean interval or Proportion interval.
- Choose a confidence level.
- Enter the sample values requested by that mode.
- Press Calculate interval and review the bounds and formula steps.
Best uses
Start here if one of these sounds like your job. The examples below show which inputs matter most.
- Calculate a confidence interval for a mean using standard deviation and sample size.
- Calculate a confidence interval for a sample proportion.
- Compare common confidence levels from 80% through 99%.
- Copy the interval, margin of error, z-score, and point estimate.
Mean intervals
Mean mode uses the sample mean, standard deviation, and sample size to estimate a range around the mean.
The calculator shows the standard error and z critical value used in the margin of error.
Proportion intervals
Proportion mode uses successes divided by sample size as the point estimate.
The interval is clipped to stay within 0% and 100% because proportions cannot fall outside that range.
Worked examples for Confidence Interval Calculator
67.02 to 68.98
42.2% to 61.8%
67.1775 to 68.8225
FAQ in plain language
What is a confidence interval?
A confidence interval is a range around a sample estimate that is built to capture a population value at a chosen confidence level.
What interval types are supported?
This version supports z intervals for a single mean and a single proportion.
What do the main Confidence Interval Calculator inputs mean?
The main inputs are the numbers, operation, mode, or known values the calculator needs. Keep units consistent, enter percentages the way the page label shows, and use the examples as a quick check before trusting the answer.
How should I read the Confidence Interval Calculator answer?
Read the headline answer, then check the supporting lines and examples to understand how the calculator got there. If one input changes, rerun the tool and compare the new answer instead of guessing.
What should I double-check before trusting the Confidence Interval Calculator?
Check units, signs, rounding, and the selected mode before copying the answer. If the number feels weird, rerun one of the examples first, then put your own values back in slowly.
What is margin of error?
Margin of error is the amount added to and subtracted from the point estimate to create the lower and upper bounds.
Should I use mean or proportion mode?
Use mean mode for numeric averages. Use proportion mode for successes out of a total, such as yes responses or defect counts.
Sources
Use these if you want to compare the formula, inputs, or limits with a trusted outside explanation.
Related tools
- Sample Size Calculator Estimate survey sample size from confidence level, margin of error, and proportion.
- Z-score Calculator Calculate a z-score and approximate standard normal percentile.
- Statistics Calculator Calculate count, sum, mean, median, mode, range, quartiles, variance, and standard deviation.
Keep exploring
If this guide is close but not exact, these links keep you near the same kind of problem.
- Calculators Browse the full category for related tools that help with the same job.
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- All calculator and utility guides Find more plain-language examples, formulas, mistakes, and result explanations.
- Free calculator resources Start here when you are not sure which calculator page fits.
Privacy and copying results
Recent answers stay visible only while you work in the current browser tab. They are not sent to a server.
Use Copy answer when you want to save the inputs and result in notes, homework, a message, or a project list. Check the units, labels, and limits before copying.