Standard normal formula
z = (x − μ) / σ
For a standard normal distribution, μ = 0 and σ = 1. The left-tail probability is the cumulative area under the curve up to z.
Example
If z = 1.0, the cumulative probability is about 0.8413, meaning 84.13% of values fall below that point.
Frequently Asked Questions
What is a z-score?
A z-score tells how many standard deviations a value is from the mean.
What is a normal distribution?
It is a bell-shaped distribution common in statistics, where data cluster around the mean.
Does this use the standard normal table?
Yes, the calculator uses the standard normal cumulative approximation so the probabilities are accurate for practical use.