The Excel CONFIDENCE function returns the margin of error for a population mean, using the normal distribution. It is the legacy name of CONFIDENCE.NORM, introduced in Excel 2010.
Syntax
| Argument | Description | |
|---|---|---|
alpha | Required | The significance level used to compute the confidence level (the confidence level is 1 − alpha; 0.05 gives 95%). |
standard_dev | Required | The population standard deviation for the data range (assumed known). |
size | Required | The sample size. |
How to use it
CONFIDENCE returns the half-width of a confidence interval for a mean: take the sample mean and add ± this value to get the interval. It assumes a known population standard deviation and uses the normal (z) distribution.
An alpha of 0.05 corresponds to a 95% confidence level. If the population standard deviation is unknown and you have a small sample, the t-based CONFIDENCE.T is more appropriate.
Use CONFIDENCE.NORM instead: =CONFIDENCE.NORM(0.05,2.5,50) in Excel 2010+ returns the same margin. The newer family also adds CONFIDENCE.T for the small-sample, unknown-sigma case.
Try it: interactive demo
Pick a CONFIDENCE example to see the formula and its result.
Practice workbook
Frequently asked questions
What is the modern replacement for CONFIDENCE?
CONFIDENCE.NORM, added in Excel 2010, with identical arguments. =CONFIDENCE.NORM(0.05,2.5,50) equals =CONFIDENCE(0.05,2.5,50).How do I build the confidence interval from the result?
What confidence level does alpha 0.05 give?
When should I use CONFIDENCE.T instead?
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