September 28, 2021

# How to use NORM.INV Function in Excel

The Excel NORM.INV function calculates the inverse of the Cumulative Normal Distribution Function for a supplied value of x, and a supplied distribution mean & standard deviation.

Syntax:= NORM.INV(probability,mean,standard_dev)

The NORM.INV function syntax has the following arguments:

• Probability     Required. A probability corresponding to the normal distribution.
• Mean     Required. The arithmetic mean of the distribution.
• Standard_dev     Required. The standard deviation of the distribution.

Example: Let’s look at some Excel NORM.INV function examples and explore how to use the NORM.INV function as a worksheet function in Microsoft Excel:

Example 1:

Let’s say, you work in a mobile phone company. On an average, the battery fails after 1200 days with standard deviation of 120.

Find the the days by which 6.5% (0.065) of batteries will fail. Syntax:  =NORM.INV(B1,B2,B3)

Result: 1018.307773 The above formula returns 1018.307773. It means 6.5% of batteries will expire within 1018 days. It is the ICDF of 0.065 in above example. The manual calculation is really complex. Excel NORM.INV function makes it simple.

Example 2: Find the the days by which 6.5% (0.065) of batteries will survive.

Now we need to calculate the number of days by which 6.5% batteries will survive. To do so we need to calculate ICDF of 93.5% of Failure. This will be the number of days by which 6.5% batteries will survive. This returns 1381.692227. This means 6.5% of batteries will survive after 1381.7 days.

Note:

1. If the mean equals zero and the standard deviation equals 1, NORM.INV uses the standard normal distribution.
2. #VALUE! error – Occurs if any of the given arguments is non-numeric.
3. #NUM! error – Occurs when:
• The given probability argument is less than zero or greater than one.
• The given standard_dev argument is less than or equal to zero.
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