Collabora Office TDIST: One-tail and two-tail Student probabilities
Use TDIST tail-count mode correctly, distinguish it from T.DIST density/CDF mode and handle nonnegative input and degrees of freedom.
Verification status: See the evidence and test scope described in this guide. How formula examples are checked
Quick answer: =TDIST(1;1;1) independently gives 0.25, the upper-tail probability beyond t = 1 with one degree of freedom. Changing the final argument to 2 gives 0.5, the combined probability in both tails beyond ±1. The final argument counts tails, not density versus CDF.
Syntax and direction
=TDIST(Number; DegreesFreedom; Mode)
Number must be nonnegative. Mode 1 calculates the right-tail probability P(T≥Number); Mode 2 calculates P(|T|≥Number). The official TDIST help describes these as one-tailed and two-tailed modes. There is no omitted-mode default in this evaluator.
DegreesFreedom and Mode are floored before validation. DegreesFreedom must then be at least 1 and Mode must be 1 or 2. Use explicit whole numbers. A positive fractional mode is not a third statistical interpretation; it can silently floor to a different valid choice.
A tail probability is neither the t statistic itself nor a probability that a null hypothesis is true. The suitability of a t reference distribution depends on the statistic and assumptions that produced it.
Worked example: a simple exact tail calculation
Enter B2 = 1, B3 = 1 and B4 = 1. Use =TDIST(B2;B3;B4). With one degree of freedom the t distribution is the standard Cauchy distribution, whose upper tail is 0.5−atan(t)/π.
At t = 1, atan(1)=Ï€/4, so the independently calculated right tail is 0.25. Mode 2 doubles this by symmetry to 0.5. The corresponding left CDF is 0.75, a third quantity that is not requested by TDIST Mode 1.
At t = 0, the upper tail is 0.5 and the two-tail probability is 1. The formulas =TDIST(0;1;1) and =TDIST(0;1;2) therefore give those independent reference values.
For a second check, =TDIST(1;2;1) independently gives approximately 0.2113248654. For two degrees of freedom the upper-tail expression is 0.5×(1−t/sqrt(t²+2)). This shows why changing the degrees of freedom changes the result even at the same t coordinate.
Advanced use: preserve the sign of a directional test
For a two-sided statistic t = −1 with one degree of freedom, =TDIST(ABS(-1);1;2) correctly expresses the model probability outside ±1, giving 0.5. The absolute value is appropriate because the requested event is two-sided.
For an upper-tail directional question at t = −1, the probability is instead 0.75, by symmetry. Passing −1 directly to legacy TDIST is rejected. Computing TDIST(ABS(-1);1;1) would give 0.25 and answer the wrong direction. A source-consistent symmetry expression for this specific case is =1-TDIST(1;1;1).
Choose the tail according to the question before seeing the result; do not change direction merely to obtain a smaller probability. The formulas here illustrate distribution mechanics, not a complete test of any particular dataset. If the t statistic was calculated from a sample, its degrees of freedom must come from that procedure rather than from this function.
Errors and differences from modern names
=TDIST(-1;1;1) follows internal IllegalArgument. The same occurs for a mode of 3 or degrees of freedom zero. =TDIST(1;1.9;1.9) instead uses floored values 1 and 1 and predicts 0.25. This accepted conversion is not a recommendation to use noninteger modes.
The legacy wrapper and GetTDist helper establish the nonnegative domain and one/two-tail calculations. T.DIST uses a Boolean density/CDF selector instead. Replacing only the name while keeping the third argument can therefore reverse the statistical meaning.
T.DIST.RT and T.DIST.2T have their own two-argument contracts. This guide does not claim that all these spellings share the same domain over negative inputs. Native application results, localized errors and extreme-tail precision have not been tested; the reference examples use exact or elementary formulas.
Product scope, compatibility and evidence
This guide covers the new Collabora Office desktop for Linux, using the Flathub source tag coda-26.04.4.3-1 and commit 81339d176148d0d5c81ff05d82540f58f8aaa117. The official desktop release notes and Linux package manifest identify that product/build. The package manifest is a dated observation from October 18, 2026, rather than an installed-binary check.
The 26.04 function help and exact evaluator source were inspected on October 18, 2026. Expected examples were independently calculated; no Collabora application was run. Expected scalar results were derived from the documented contracts, inspected source and independent calculations; native output formatting and error localization have not been tested. Classic, Online/CODE, other operating systems and file-format round trips require their own checks.
Availability here is established from the function-specific help and the mapped package source. Related functions may have different arguments or boundary rules. The first Collabora release introducing this function is not established by the reviewed sources. No cited retirement or deprecation notice was found. Unknown introduction dates do not imply that the function is deprecated. File-format round trips require separate verification.