The Excel T.INV.2T function returns the two-tailed inverse of the Student's t-distribution — the positive t-value that leaves a given probability split equally between both tails.
Syntax
| Argument | Description | |
|---|---|---|
probability | Required | The total two-tailed probability, between 0 and 1 (split evenly across both tails). |
deg_freedom | Required | The degrees of freedom (a positive integer). |
How to use it
T.INV.2T answers “what critical t leaves probability in the two tails combined?” — the value you use for a two-sided confidence interval or a non-directional t-test.
It always returns a positive number, and it relates to the left-tailed T.INV by T.INV.2T(p, df) = T.INV(1 − p/2, df).
Pick the level by alpha: for a 95% two-sided interval pass 0.05; for 99% pass 0.01. The function does the “divide alpha between the tails” bookkeeping for you.
Try it: interactive demo
Pick a T.INV.2T example to see the formula and its result.
Practice workbook
Frequently asked questions
What does T.INV.2T return?
How does T.INV.2T relate to T.INV?
T.INV.2T(p, df) = T.INV(1 − p/2, df). The two-tailed version puts half the probability in each tail, so it converts to a left-tail lookup of 1 − p/2.What probability do I pass for a 95% interval?
Does T.INV.2T ever return a negative number?
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