How it's calculated
critical value = F⁻¹(1 − α/2) (two-tailed)
F⁻¹ = inverse CDF (quantile) of the chosen distribution (z, t, χ² or F), α = significance level. One-tailed uses 1 − α (or α); χ² and F use the right tail. df sets the t / χ² / F shape.
Common questions
What is a critical value?
It is the cutoff point a test statistic must pass for you to reject the null hypothesis at your chosen significance level.
Why do I need degrees of freedom?
The t, chi-square, and F distributions change shape with sample size, so their critical values depend on the degrees of freedom.