Returns the inverse of the cumulative beta probability density function for a specified beta distribution. That is, if probability = BETADIST(x,...), then BETAINV(probability,...) = x. The beta distribution can be used in project planning to model probable completion times given an expected completion time and variability.
Important This function has been replaced with one or more new functions that may provide improved accuracy and whose names better reflect their usage. Although this function is still available for backward compatibility, you should consider using the new functions from now on, because this function may not be available in future versions of Excel.
For more information about the new function, see BETA.INV function.
Syntax
BETAINV(probability,alpha,beta,[A],[B])
The BETAINV function syntax has the following arguments (argument: A value that provides information to an action, an event, a method, a property, a function, or a procedure.):
 Probability Required. A probability associated with the beta distribution.
 Alpha Required. A parameter of the distribution.
 Beta Required. A parameter the distribution.
 A Optional. A lower bound to the interval of x.
 B Optional. An upper bound to the interval of x.
Remarks
 If any argument is nonnumeric, BETAINV returns the #VALUE! error value.
 If alpha ≤ 0 or beta ≤ 0, BETAINV returns the #NUM! error value.
 If probability ≤ 0 or probability > 1, BETAINV returns the #NUM! error value.
 If you omit values for A and B, BETAINV uses the standard cumulative beta distribution, so that A = 0 and B = 1.
Given a value for probability, BETAINV seeks that value x such that BETADIST(x, alpha, beta, A, B) = probability. Thus, precision of BETAINV depends on precision of BETADIST.
Example
The example may be easier to understand if you copy it to a blank worksheet.
How do I copy an example?
 Select the example in this article. If you are copying the example in Excel Online, copy and paste one cell at a time.
Important: Do not select the row or column headers.
Selecting an example from Help
 Press CTRL+C.
 Create a blank workbook or worksheet.
 In the worksheet, select cell A1, and press CTRL+V. If you are working in Excel Online, repeat copying and pasting for each cell in the example.
Important: For the example to work properly, you must paste it into cell A1 of the worksheet.
 To switch between viewing the results and viewing the formulas that return the results, press CTRL+` (grave accent), or on the Formulas tab, in the Formula Auditing group, click the Show Formulas button.
After you copy the example to a blank worksheet, you can adapt it to suit your needs.

A 
B 
Data 
Description 
0.685470581 
Probability associated with the beta distribution 
8 
Parameter of the distribution 
10 
Parameter of the distribution 
1 
Lower bound 
3 
Upper bound 
Formula 
Description (Result) 
=BETAINV(A2,A3,A4,A5,A6) 
Inverse of the cumulative beta probability density function for the parameters above (2) 
