This P-Value Calculator computes the probability value (p-value) from a given Z-score using the standard normal distribution.
Users can select between a one-tailed or two-tailed hypothesis test. The calculator uses the error function erf() to evaluate the normal cumulative distribution function (Φ), then applies the correct tail formula:

• One-Tailed Test: p = 1 − Φ(|z|)
• Two-Tailed Test: p = 2 × (1 − Φ(|z|))

It displays the Z-score, chosen test type, and the computed p-value (up to six decimal places), along with a short interpretation note.
You can use this code directly as an HTML page or paste it into a WordPress HTML block — it will work perfectly without modification.