Z-Score Calculator

A z-score says how many standard deviations a value sits from the mean of a normal distribution. Enter a raw value with its mean and standard deviation to get the z-score, or enter a z-score directly, and either way you get the percentile, the area to the left and to the right of the curve, and the two-tailed p-value. The normal distribution function is evaluated with Hart's rational approximation, so the probabilities hold well past the six decimals shown. It assumes the data really is normally distributed, which is worth checking before reading much into the percentile.