Z-Score Calculator
Calculate the z-score, p-value, and percentile rank for any data point.
Results
Z-score
0.5000
(x − μ) / σ
Percentile
69.15%
of values below x
P (left tail)
0.6915
P(X ≤ x)
P (right tail)
0.3085
P(X > x)
Two-tailed p-value: 0.6171
Interpretation: Z = 0.50 is not statistically significant at α = 0.05.
How z-scores and p-values work
A z-score (standard score) measures how many standard deviations a value is from the mean: z = (x − μ) / σ. A z-score of 0 means the value equals the mean; ±1 is one standard deviation away. The p-value (left tail) gives the probability that a randomly sampled value would be less than or equal to x — the percentile rank. Two-tailed p-value covers both extremes.
For standard deviation, try the Standard Deviation Calculator. For general statistics, see Average Calculator.
Private & free — this tool runs entirely in your browser.