Generating count variable for observations per year

I have the following (simplified) dataset

Person_ID	Fiscal_Year
101	2015
101	2015
101	2016
102	2016
102	2017
102	2017
103	2015
103	2016
103	2017

I would like to generate a variable that counts the Person_ID's per Fiscal year.
So, for example, the variable should contain the value 2 because the person ID is two times in the Fiscal_Year 2015.

The values of the new variable should be as follows:

Person_ID	Fiscal_Year	New_Variable
101	2015	2
101	2015	2
101	2016	1
102	2016	1
102	2017	2
102	2017	2
103	2015	1
103	2016	1
103,	2017	1

Could anyone help me out?

Thnx in advance!