Student t CDF calculator

Reviewed by the CalculatorHub team, edited by James Graham. Method from NIST/SEMATECH e-Handbook of Statistical Methods. Last verified 2026-06-23.

The Student t CDF calculator computes student t cdf from the relation P(T<=t) via regularized incomplete beta. It takes 2 inputs (t value, degrees of freedom) and returns the cumulative probability. Because this is a pure mathematical or physical formula rather than a jurisdiction-specific rule, the result never changes over time: the same inputs always produce the same answer, so you can rely on it whether you are checking homework, sizing a design, or sanity-checking another tool. Enter your values in the fields below and the result updates instantly; you can also share a permalink that pre-fills the exact calculation, which is useful for teaching, reports, or collaboration. For example, with t value = 2, degrees of freedom = 10, the cumulative probability works out to 0.963306, and the worked example further down the page shows every step so you can follow the arithmetic and reproduce it by hand. The method is the standard form documented by NIST/SEMATECH e-Handbook of Statistical Methods, and the figure above each result carries the date it was last verified. This tool is general information and is not a substitute for professional engineering, medical, financial, or scientific advice; always check critical results against the primary source and your own judgement.