Normalcdf Calculator
Compute the cumulative distribution function (CDF) for a normal distribution. Given a mean, standard deviation, and a value x, find the probability that a random variable is less than or equal to x.
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isCalculator Editorial Team
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How to Use the NormalCDF Calculator
This calculator computes the probability that a normally distributed random variable X is less than or equal to a given value x, i.e., P(X ≤ x).
- Enter the Mean (μ) – The average of your distribution (e.g., 0).
- Enter the Standard Deviation (σ) – Must be a positive number (e.g., 1).
- Enter the Value (x) – The cutoff point for the cumulative probability (e.g., 1.96).
- Click "Calculate Probability" – The result shows the probability and the Z-score calculation steps.
Note: All inputs accept decimal numbers. Standard deviation must be greater than zero. The result is rounded to 6 decimal places.
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Frequently Asked Questions
It computes the probability that a normally distributed random variable is less than or equal to a given value x, using the cumulative distribution function.
You need the mean (μ), standard deviation (σ), and the value x. All must be real numbers, with σ > 0.
The calculator first computes the z-score: z = (x - μ)/σ, then uses an approximation to the standard normal CDF to find the probability.
