TINV function
Returns the twotailed inverse of the Student's tdistribution.
Important This function has been replaced with one or more new functions that may provide improved accuracy and whose names better reflect their usage. This function is still available for compatibility with earlier versions of Excel. However, if backward compatibility is not required, you should consider using the new functions from now on, because they more accurately describe their functionality.
For more information about the new functions, see T.INV.2T function or T.INV function.
Syntax
TINV(probability,deg_freedom)
The TINV function syntax has the following arguments:

Probability Required. The probability associated with the twotailed Student's tdistribution.

Deg_freedom Required. The number of degrees of freedom with which to characterize the distribution.
Remarks

If either argument is nonnumeric, TINV returns the #VALUE! error value.

If probability <= 0 or if probability > 1, TINV returns the #NUM! error value.

If deg_freedom is not an integer, it is truncated.

If deg_freedom < 1, TINV returns the #NUM! error value.

TINV returns that value t, such that P(X > t) = probability where X is a random variable that follows the tdistribution and P(X > t) = P(X < t or X > t).

A onetailed tvalue can be returned by replacing probability with 2*probability. For a probability of 0.05 and degrees of freedom of 10, the twotailed value is calculated with TINV(0.05,10), which returns 2.28139. The onetailed value for the same probability and degrees of freedom can be calculated with TINV(2*0.05,10), which returns 1.812462.
Note In some tables, probability is described as (1p).
Given a value for probability, TINV seeks that value x such that TDIST(x, deg_freedom, 2) = probability. Thus, precision of TINV depends on precision of TDIST. TINV uses an iterative search technique. If the search has not converged after 100 iterations, the function returns the #N/A error value.
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.
Important Do not select the row or column headers.
Selecting an example from Help

Press CTRL+C.

In Excel, create a blank workbook or worksheet.

In the worksheet, select cell A1, and press CTRL+V.
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.

