How to Calculate a Two-Tailed P-Value with T.DIST.2T in Excel

Use T.DIST.2T to test whether a change made any difference — up or down — such as a website redesign.

You will learn to

• Get a two-tailed p-value from a t-score
• Handle negative t-scores with ABS
• Run a paired test from summary numbers

How it works

A two-tailed test asks "did anything change, in either direction?" — the usual question after a redesign, a new process or a price change. T.DIST.2T(t,df) returns the probability of a result at least as extreme as t on either side, which is the two-tailed p-value.

T.DIST.2T only accepts t of zero or more (a negative t returns #NUM!), so wrap the t-score in ABS. For before/after data on the same items, compute t from the average difference: mean ÷ (SD ÷ √n), with n − 1 degrees of freedom.

=T.DIST.2T(2.25,38)