TINV function
Returns the tvalue of the Student's tdistribution as a function of the probability and the degrees of freedom.
Syntax
TINV(probability,degrees_freedom)
Probability is the probability associated with the twotailed Student's tdistribution.
Degrees_freedom is 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 degrees_freedom is not an integer, it is truncated.

If degrees_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, degrees_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 to copy an example

Create a blank workbook or worksheet.

Select the example in the Help topic.
Note Do not select the row or column headers.
Selecting an example from Help

Press CTRL+C.

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

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.

