P-value Calculator

Supports Z (standard normal), t, χ² (chi-square), and F distributions. Choose tail: left, right, or two-tailed.

Drag & drop a .txt/.csv here (or click) to auto-fill fields.
Examples it understands: z=2.05, t=2.13, df=18, chi2=7.9, df=3, f=4.1, df1=2, df2=20

Distribution

Tail

Test statistic (x)

For Z: no df. For t/χ²: use df. For F: use df₁, df₂.

P-value Calculator — Quick Cheat Sheet

Z (Normal) — no df. Right-tail: P(Z ≥ z), Left-tail: P(Z ≤ z), Two-tail: 2·min(P(Z ≤ z), P(Z ≥ z)).
t — requires df. Heavier tails than normal for small df.
χ² — requires df, support x ≥ 0. Commonly right-tailed tests.
F — requires df₁, df₂, support x ≥ 0. Typically right-tailed.
Two-tailed p is 2·min(CDF(x), 1−CDF(x)) except for inherently one-sided tests (use right/left as appropriate).
Rounding: show p in scientific notation for very small values (e.g., 3.2e−7).
Validate df: df must be positive; F uses both df₁ and df₂.

Math details (implementation)

Normal CDF via erf approximation (Abramowitz–Stegun style).
t/F CDFs via regularized incomplete beta I_x(a,b).
χ² CDF via regularized lower incomplete gamma P(k/2, x/2).
Numeric safeguards (domain checks, symmetry) are applied for stability.

P-value Calculator

P-value Calculator — Quick Cheat Sheet

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