Returns the Percentage Points (probability) for the Student tdistribution where a numeric value (x) is a calculated value of t for which the Percentage Points are to be computed. 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
TDIST(x,degrees_freedom,tails)
X is the numeric value at which to evaluate the distribution.
Degrees_freedom is an integer indicating the number of degrees of freedom.
Tails specifies the number of distribution tails to return. If tails = 1, TDIST returns the onetailed distribution. If tails = 2, TDIST returns the twotailed distribution.
Remarks

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

If degrees_freedom < 1, TDIST returns the #NUM! error value.

The degrees_freedom and tails arguments are truncated to integers.

If tails is any value other than 1 or 2, TDIST returns the #NUM! error value.

TDIST is calculated as TDIST = p( x<abs(X)), where X is a random variable that follows the tdistribution.
Examples
X 
Degrees 
Formula 
Description (Result) 
1.96 
60 
=TDIST([X],[Degrees],2) 
Twotailed distribution (0.054644927 or 5.46 percent) 
1.96 
60 
=TDIST([X],[Degrees],1) 
Onetailed distribution (0.027322463 or 2.73 percent) 