Microsoft Excel for statistics > Normal Distribution Probability in Excel

Before you begin, you might find it helpful to review what a normal distribution is. See: What is a normal distribution?

You can also review what different types of word problems you’re likely to come across. See:

Normal distributions Word Problems.

Watch the video, or read the steps below:

## How to Calculate Normal Distribution Probability in Excel

While it’s possible to look up probabilities for a normal distribution using the z-table, it’s actually much easier to calculate probabilities in Excel for a couple of reasons. First, there’s no looking at a table; the **NORMDIST function** does the hard work for you. Second, Excel does the intermediate calculations for you. Most calculation errors happen in an intermediate step (such as calculating the z-score to look up) rather than the actual z-score itself. Excel can handle three types of probability calculations: more than, less than, and in between. These instructions work for Excel 2007 and Excel 2010.

**Sample Question:** Suppose that a contaminant in samples from a city’s water supply has a mean of 500 ppm and a standard deviation of 100 ppm. What is the probability that bacteria in a randomly selected water sample will be: 1/ **less than** 600 ppm 2/**More than **600 ppm 3/**between **400 and 600 ppm?

### Calculate Normal Distribution Probability in Excel: Less than

Step 1:** Click an empty cell**.

Step 2:** Click “Insert Formula”**.

Step 3:** Type “Normdist” into the search box **and then click “Go.”

Step 4:** Select “NORMDIST” from the list and then click “OK”** to open the Function Arguments window.

Step 5:** Enter your data into the box.** For this example, type “600” in the X box, “500” in the Mean box, “100” in the Standard Deviation box and “true” in the cumulative box..

Step 6:** Click “OK.”**. This returns 0.84134474 in the cell you clicked in Step 1, which is the probability of getting under 600 ppm.

### Calculate Normal Distribution Probability in Excel: More than

Step 7:** Subtract your answer from Step 7 (above) from 1:**

1-0.84134474= 0.158653.

### Calculate Normal Distribution Probability in Excel: Between

Step 8:** Repeat Steps 1 through 8 **for the second value, which for this example is 400. The probability is 0.15865526.

Step 9:** Subtract the larger probability from the smaller probability.** In this example:

0.84134474 – 0.15865526 = 0.68269

*That’s it!*

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