P-value Calculator

Two-tailed normal p-value from a z-score (approximation).

P-value Calculator helps you two-tailed normal p-value from a z-score (approximation). Enter z-score, review the breakdown, and use the guidance below to understand what the number means — and what it does not. What the P-value calculator does P-value Calculator is built for arithmetic, algebra, geometry, and number tools. Two-tailed normal p-value from a z-score (approximation). You enter z-score, then Simple Calculators computes the result instantly. Results use standard school and engineering formulas that run privately in your browser. How the math works Enter the Z-score from your test. The calculator finds the share of a normal (bell-shaped) curve lying beyond your z-score, using a standard approximation that is accurate to about 7 decimal places. The two-tailed p-value counts both ends of the curve: p = 2 × (1 − area below |z|), where |z| means z without its minus sign. It also gives the one-tailed p-value and says whether the result is significant at the 10%, 5%, 1% and 0.1% levels. The formula: p = 2 × (1 − Φ(|z|)). Φ(z) is the share of a normal bell curve below z. The p-value is the chance of a result at least this far from average in either direction.