Related Function:

The CONFIDENCE.NORM function returns the confidence interval for a population mean, using a normal distribution.

  • This function was introduced in Excel 2010 and so is not available in earlier versions.
  • CONFIDENCE.NORM and CONFIDENCE.T functions replace the CONFIDENCE function included in earlier versions of Excel.




Argument Description
alpha The significance level used to compute the confidence level

  The confidence level equals 100*(1 – alpha)%, i.e. an alpha of 0.05 indicates a 95 percent confidence level
standard_dev The standard deviation of the population
size The population sample size


  A B C D
1 Data Description    
2 0.05 Significance level    
3 2.5 Standard deviation    
4 100 Sample size    
6 Formula Result Notes
7 =CONFIDENCE.NORM(A2,A3,A4) 0.489991 Confidence interval for a population mean

Usage note: To calculate the confidence interval for a population mean, the returned CONFIDENCE value must then be added to, and subtracted from, the sample mean. I.e. for the sample mean \bar{x}:    

    \[    \text{Confidence Interval} = \bar{x} \pm \text{CONFIDENCE}    \]

In the example above, the CONFIDENCE.NORM function is used to calculate the confidence interval, with a significance of 0.05 (confidence level of 95%), for the travel time to work for a sample population of 100 people. The sample mean is 30 minutes and the standard deviation is 2.5 minutes. 

Therefore, the confidence interval is 30 \pm 0.489991, which is equal to a drive time of 30 ± 0.489991 minutes, or 29.5 to 30.5 minutes.

Common Function Error(s)

Problem What went wrong
#VALUE! Occurs if any of the supplied arguments are non-numeric
#NUM! Occurs if either:

  the supplied alpha is ≤ 0 or ≥ 1
  the supplied standard_dev is ≤ 0
  the supplied size argument is < 1

In statistics, the confidence interval is the range of values into which a population parameter is likely to fall, for a given probability. That is, a sample mean (x) is at the center of the range and the range is x ± CONFIDENCE.NORM.

For example, for a given population and a probability of 95%, the confidence interval is the range, in which a population parameter is 95% likely to fall.

Note that the accuracy of the confidence interval relies on the population having a normal distribution.

See Wikipedia for more information on confidence interval