TDIST in ONLYOFFICE: Legacy One- or Two-Tail Student t Probability

Create TModel. Put Parameter in A1 and Value in B1. Enter Threshold in A2 and 1 in B2; Degrees of freedom in A3 and 1 in B3; Tail area in A4 and 0.05 in B4. Keep these cells unchanged when adding controls.

One degree of freedom is chosen because the t distribution then has the Cauchy closed form: its CDF is 1/2+atan(t)/π and its density is 1/[π(1+t²)]. This lets the examples be checked independently without running ONLYOFFICE. It is an arithmetic teaching case, not a recommendation to base practical inference on a tiny sample.

A t distribution is symmetric around zero. Its tail heaviness depends on degrees of freedom; a t value is not a raw measurement in minutes or grams. In a statistical test, its construction and degrees of freedom must come from the appropriate sampling model. A distribution formula alone does not establish those assumptions.

The official reference takes a nonnegative threshold, degrees of freedom and tails equal to 1 or 2. One tail means the upper tail beyond the supplied positive magnitude; two tails means the total beyond ±that magnitude.

The same third-position argument in modern T.DIST has a completely different role. =T.DIST(1,1,TRUE) targets a left CDF of 0.75. Replacing TDIST with T.DIST while leaving a final 1 would not preserve the original 0.25 event in the inspected implementation.

At df=1, the right tail is 1/2−atan(x)/π. At x=1, it equals 1/4, and the two-tail area is twice that. At zero, the source accepts the boundary and returns 1/2 or 1 even though the help’s short domain description says x greater than zero.

For nonnegative x, TDIST(x,df,1) maps mathematically to T.DIST.RT, and TDIST(x,df,2) maps to T.DIST.2T. Those interfaces make the tail interpretation explicit without a numeric tails argument.

A negative signed statistic needs special care. TDIST rejects negative x, whereas T.DIST.RT accepts a signed threshold. For a prespecified right-sided test at x=−1, the right-tail area is 0.75 at df=1. Passing ABS(−1) to TDIST with one tail instead gives 0.25 and loses the direction. For a two-sided magnitude question, using ABS can be appropriate, but it changes what is being asked.

The legacy probability is not a chance that a null hypothesis is true, and a small value does not establish practical significance. Degrees of freedom and the statistic must follow from an appropriate procedure. T.TEST provides paired or independent-sample calculations, but its one-tail implementation also has direction-related limitations.

The code requires x≥0, df≥1 and the numeric tails value exactly equal to 1 or 2. A fractional tails argument such as 1.9 is not parsed to 1 here; it is source-predicted #NUM!. Negative x and df=0 also give #NUM!. Conversion failures propagate before the tail calculation.

Help calls df an integer, but this forward implementation does not explicitly truncate the df value before the common helper. Inverse t functions do apply parseInt. The examples use integer df and do not claim a universal conversion rule across the family.

Both legacy tail choices use the beta-based common helper. The mathematical two-tail/one-tail ratio is 2 for nonnegative inputs, but finite precision limits extreme parameters. Avoid unbounded exploratory inputs and do not read a rounded tail of zero as certainty. Source array preparation is not a native spill or workbook-import test.

The original introduction version and final supported-version endpoint are unknown from the checked references. Legacy naming by itself does not prove removal, deprecation or complete compatibility with another spreadsheet product.

Checked October 18, 2026 against current official help and SDKJS tag v10.0.0.169, commit 3679e0375a758d7dc59d31337a45461be3525ed8. Introduction dates and a final supported-version endpoint are not established. Desktop Editors, Docs, mobile releases and imported files require separate compatibility checks.

Neither the ONLYOFFICE application nor its calculation engine was executed for this guide. The numerical targets are independently calculated mathematical values; code-path and error observations are manual source traces. They are not screenshots, displayed workbook results or promises of identical final digits. Use English function names and comma separators as shown, adapting separators to the editor’s locale.

Keep inputs and intermediate probabilities numeric and unrounded. Format the display rather than replacing values with rounded strings. These moderate scalar examples do not certify extreme-tail accuracy, unusual type coercion, array entry or dynamic spill. Model assumptions must be checked separately from arithmetic correctness.

• Official TDIST help, checked October 18, 2026.
• Pinned function definition.
• T-probability helper, inverse solver and test calculations.
• T.DIST.
• T.DIST.2T.
• T.DIST.RT.
• T.INV.
• T.INV.2T.
• T.TEST.