Normal Distribution: P(Z ≤ 2.576)
P(Z ≤ 2.576) ≈ 0.9950, used as the critical z-value for 99% confidence intervals.
How to use this tool
- Enter z-score in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your p(z ≤ z) — cumulative probability and the full breakdown beneath it.
Calculate the cumulative normal probability at z = 2.576, the critical value used in 99% confidence interval calculations.
Frequently asked questions
- What does Φ(z) represent?
- Φ(z) is the cumulative distribution function of the standard normal distribution — the probability that a standard normal random variable is less than or equal to z. For example, Φ(1.96) ≈ 0.975, corresponding to the 95% confidence interval.