Free interactive student tool
Free Confidence Interval Calculator
Free Confidence Interval Calculator. Mean, proportion, difference and variance modes; state assumptions.
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Estimate ± critical value × standard error
How this tool reaches its result
A mean confidence interval combines the sample mean, standard deviation, sample size and confidence level.
Estimate ± critical value × standard error
Worked context
How to interpret the output
Larger samples generally narrow the interval when variability is unchanged.
Important limitation
What the result cannot decide for you
The interpretation concerns the estimation procedure, not the probability that a fixed computed interval contains the parameter.