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Normal Distribution Calculator
Find probabilities under the normal curve for any mean and standard deviation.
Normal curve probabilities
Probability: —
As a percentage: —
Z score: —
Complement: —
How to use the Normal Distribution Calculator
- Enter the mean and standard deviation of your distribution.
- Choose the probability you want and type the value or values to test.
- Read the probability, percentage, z score and complement in the result panel.
Features
- Probabilities below, above, between and outside
- Z score for the values you enter
- Complement probability and percentage
- Runs locally, no uploads
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Frequently Asked Questions
Common questions about the free online normal distribution calculator.
Enter the mean, standard deviation and value, then choose whether you want the probability
below, above or between values.
A z score says how many standard deviations a value sits from the mean. The tool converts
your value into one automatically.
It is about 0.975, which is why the range from minus 1.96 to 1.96 holds roughly 95 percent of
the normal curve.
It is the normal curve with a mean of zero and a standard deviation of one, used as the
reference for every z score.
Many measurements and sample means follow it closely, which makes it the basis for confidence
intervals and hypothesis tests.
It is one minus the probability you asked for, so it gives the chance of the opposite outcome
under the same curve.
Yes. Enter any values, including negative means and decimals, and the tool standardises them
before finding the probability.
They are computed from a standard numerical approximation of the normal curve and are
accurate to about six decimal places.
No. Every calculation runs locally in your browser, so your numbers never leave your device.
Yes. It is completely free and unlimited, with no account, no sign-up and no usage limits of
any kind.
Last updated: October 10, 2026