Group data for the last twelve months.

i have 4 years of data and would like to select the last twelve months.
Steps ive taken so far:
-Turn my data into a table
-I created a pivot table using the table i just created
-Right Clicked on a date cell of the pivot table and chose group.
-Start date is twelve months ago and End date, today. By: Months.
-Dates showing (jan - dec) although the start date was in june...

Not sure whats happening there.

Thank you!

exactly what i needed thank you!