Work out standard normal probability instantly with clear inputs, formula shown and shareable results.
The standard normal distribution has mean 0 and standard deviation 1. Its cumulative distribution Φ(z) gives the area to the left of z, and every other region follows by symmetry and subtraction.
Standard normal CDF
Φ(z) = ½[1 + erf(z/√2)]
Symmetry
Φ(−z) = 1 − Φ(z)
About 0.975, which is why ±1.96 brackets the central 95% of a normal distribution.
Standardise first: z = (x − μ)/σ, then read the same table.