# The Excel CHIINV Function

CHIINV and CHISQ.INV.RT

In Excel 2010, the Chiinv function has been replaced by the Chisq.Inv.Rt function, which has improved accuracy.

Although it has been replaced, the Chiinv function is still available in Excel 2010 (stored in the list of compatibility functions), to allow compatibility with earlier versions of Excel.

However, the Chiinv function may not be available in future versions of Excel, so it is advised that you use the Chisq.Inv.Rt function if possible.

Related Function:
CHIDIST Function

## Function Description

The Excel Chiinv function calculates the inverse of the right-tailed probability of the Chi-Square Distribution.

The syntax of the function is:

CHIINV( probability, degrees_freedom )

Where the function arguments are:

 probability - The probability of the chi-square distribution, for which you want to find the value of x. degrees_freedom - The number of degrees of freedom (must be a positive integer).(If the supplied degrees_freedom is a decimal, this is truncated to an integer).

### Relationship Between Chiinv and Chidist

The Chiinv function is the inverse of the Excel Chidist function.

I.e. for a supplied probability, the Chiinv function uses an iterative method to find the value of x such that:

Chidist ( x, degrees_freedom ) = probability

## Chiinv Function Examples

The spreadsheet below shows 5 examples of the Excel Chiinv function, used to calculate the inverse right-tailed chi-square distribution.

Formulas:
A
1=CHIINV( 0.5, 1 )
2=CHIINV( 0.75, 1 )
3=CHIINV( 0.1, 2 )
4=CHIINV( 0.8, 2 )
5=CHIINV( 0.25, 3 )
Results:
A
10.454936423
20.101531044
34.605170186
40.446287103
54.108344936

For further examples of the Excel Chiinv function, see the Microsoft Office website.

## Chiinv Function Errors

If you get an error from the Excel Chiinv function this is likely to be one of the following:

Common Errors
 #NUM! - Occurs if either:The supplied probability value is ≤ 0 or > 1;The supplied degrees_freedom argument is <1. #VALUE! - Occurs if any of the supplied arguments is non-numeric.