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BellCurve
Φ(z) — the classic bell-curve probability.
Φ(z) gives the probability that a randomly drawn value from a normal distribution falls below a given z-score — visually, it's the shaded area to the left of that point on the bell curve.
About 68% of values fall within 1 standard deviation of the mean, 95% within 2, and 99.7% within 3 — a quick mental shortcut this calculator makes precise for any z-score.
Shaded region = area to the left of z (standard normal CDF)
What you entered
Standard normal CDF at z (area to the left)
Φ(1)= 0.8413Area to the right of z
1 − 0.8413= 0.1587Result
Probability below z: 0.841
For z = 1, 84.13% of a standard normal distribution falls below this point, and 15.87% falls above.