The Excel T.INV function calculates the lefttailed inverse of the Student’s T Distribution, which is a continuous probability distribution that is frequently used for testing hypotheses on small sample data sets.
Syntax:= T.INV(probability,deg_freedom)
The T.INV function syntax has the following arguments:
 Probability Required. The probability associated with the Student’s tdistribution.
 Deg_freedom Required. The number of degrees of freedom with which to characterize the distribution.
Example: Let’s look at some Excel T.INV function examples and explore how to use the T.INV function as a worksheet function in Microsoft Excel:
Example 1:
Suppose we are given the following data:
If we want to calculate the value of the function for a probability of 0.7, the formula to use is:
Syntax: =T.INV(B1,B2)
Result: 0.568649063
So, the lefttailed inverse of the student’s tdistribution with a probability of 70% and 4 degrees of freedom is 0.568649063.
Example 2:
Suppose we are given the following data:
If we want to calculate the value of the function for a probability of 0.20, the formula to use is:
Syntax: =T.INV(B1,B2)
Result: 0.91954378
So, the lefttailed inverse of the student’s tdistribution with a probability of 20% and 10 degrees of freedom is 0.91954378.
Note:
 If either argument is nonnumeric, T.INV returns the #VALUE! error value.
 If probability <= 0 or if probability > 1, T.INV returns the #NUM! error value.
 If deg_freedom is not an integer, it is truncated.

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