TDIST Function (Gnumeric)

• Introduced: Gnumeric 0.25, explicitly named in its release notes.
• Supported in: Gnumeric 1.12.62, confirmed by its function registration. No retirement is established.
• Scope: Desktop Gnumeric with the Statistics Functions plugin. Tables use English comma-separated formulas.
• Checked: October 14, 2026. Tables were recalculated in 1.12.57 and finite reference values independently checked. Version 1.12.62 was source-checked, not executed.

With tails=1, TDIST returns the right-tail probability P(T≥x), including negative x. With tails=2 and x≥0, it returns P(|T|≥x), twice the upper tail at x. These are different questions. At x=0, one-tail probability is 0.5 and two-tail probability is 1. A negative one-tail statistic therefore need not have a small p-value. Official function reference.

=TDIST(x,dof,tails)

All arguments shown are required. The version-pinned help and evaluator establish the Gnumeric contract.

The table records the tested release’s outputs, with finite mathematical references rounded to twelve decimal places. Keep full precision when using a result in a later calculation.

For a pre-specified two-sided t test whose justified statistic is 2 with 10 degrees of freedom, put 2, 10 and 2 in A2:C2. =TDIST(A2,B2,C2) returns approximately 0.073388034771. For a one-sided upper alternative, changing C2 to 1 gives half that value. Choose the direction and number of tails before inspecting the data; switching afterward changes the test.

For a lower-tail probability at a signed statistic t, symmetry gives =TDIST(-t,dof,1). For a two-sided probability from a signed statistic use =TDIST(ABS(t),dof,2). For example, t=−1 and dof=10 give an upper-tail probability of approximately 0.829553433849, a lower-tail probability of 0.170446566151, and a two-sided probability of 0.340893132302.

Gnumeric retains fractional degrees of freedom. This is useful when a justified model, such as an unequal-variance approximation, produces a noninteger value. =TDIST(2,5.5,1) therefore does not mean “use five degrees of freedom.” The degree count must still come from the statistical method, not be adjusted to obtain a desired result.

The tails argument must be exactly 1 or 2; 1.5 is not rounded into a valid selector. Two-tail mode rejects negative x, whereas one-tail mode accepts it. Degrees of freedom below 1 are rejected without flooring accepted fractional values. TDIST only evaluates a distribution tail; it does not inspect sample independence, normality, variance assumptions or the way the statistic was constructed.

These additional outcomes were observed in the same native recalculation. F5 was genuinely empty; it is not an omitted argument. Missing inputs still need deliberate validation, even if they are converted to a numeric zero.

The worked calculations do not certify every locale, imported text value, extreme parameter or later binary version. Shared numerical helpers can change even when a function’s wrapper remains the same.

• Gnumeric function reference
• Gnumeric 1.12.62 evaluator

The reference and boundary tables use recorded 1.12.57 command-line recalculation. Further model examples were independently calculated from their stated inputs; they are not additional native test claims.