Returns the Student's lefttailed tdistribution. The tdistribution is used in the hypothesis testing of small sample data sets. Use this function in place of a table of critical values for the tdistribution.
Syntax
T.DIST(x,deg_freedom, cumulative)
The T.DIST function syntax has the following arguments:

X Required. The numeric value at which to evaluate the distribution

Deg_freedom Required. An integer indicating the number of degrees of freedom.

Cumulative Required. A logical value that determines the form of the function. If cumulative is TRUE, T.DIST returns the cumulative distribution function; if FALSE, it returns the probability density function.
Remarks

If any argument is nonnumeric, T.DIST returns the #VALUE! error value.

If deg_freedom < 1, T.DIST returns an error value. Deg_freedom needs to be at least 1.
Example
Copy the example data in the following table, and paste it in cell A1 of a new Excel worksheet. For formulas to show results, select them, press F2, and then press Enter. If you need to, you can adjust the column widths to see all the data.
Formula 
Description 
Result 
=T.DIST(60,1,TRUE) 
Student's lefttailed tdistribution for 60, returned as the cumulative distribution function, using 1 degree of freedom. 
0.99469533 
=T.DIST(8,3,FALSE) 
Student's lefttailed tdistribution for 8, returned as the probability density function, using 3 degrees of freedom. 
0.00073691 