# average inter-demand interval?

#### furious

##### New member
Can someone please explain how to calculate average inter-demand interval when you have sales data in monthly format? If someone can explain this to me with simple sample data, it is much appreciated.

Thank you so much!

#### Sambit Chakraborty

##### New member
Re: average inter-demand interval?

The average inter-demand interval (ADI) is defined as follows:
“The average interval between two demand of the spare part. It is usually expressed in periods, where the period is the referential time interval which the business utilizes for the purchases, which in your example is a month”
Assuming some sample data as follows: (Intermittent demand, several zero demand periods exist)

Month Jan Feb Mar Apr May Jun
Demand (units) 0 20 30 0 0 50

Formula for ADI = Summation of the intervals between non-zero demand periods/No. of non zero demand periods
Summation of the intervals between non-zero demand periods = From …-Feb (=1) + From Feb-Mar (=1) + From Mar-Jun (=3) = 5
No. of non zero demand periods = Feb, Mar, Jun = 3
Thus, ADI = 5/3 = 1.66, in this case.

#### furious

##### New member
Re: average inter-demand interval?

Thank You So Much! 