Rolling Sum of Revenue in Last 3 Months

Hi

I have a table in Tableau Prep with the following fields:

• Month Begin Date
• Unique Customer & Product ID
• Customer ID
• Product ID
• Revenue

I have aggregated the data so there is only one Unique Customer & Product ID for each Month Begin Date.

I want to create a calculated field called Rolling 3 Month Revenue (aka R3M Revenue)

I want the result of this field to sum Revenue for the Month Begin Date in the row, plus Month Begin Date minus 1 month and Month Begin Date minus 2 months.

I have attached an example of my desired output.

Any help would be appreciated. Thanks