I searched high and low for this and found 2 useful solutions.
1 is purely a functional one.
You can Enable Fiscal year Default & Value Date via the IMG.
Path: Financial Accounting (New)-Financial Accounting Global Settings (New)-Document-Default Values-Enable Fiscal Year Default & Default Value Date.
The second is the one that worked for me. The code below calls the function DATE_TO_PERIOD_CONVERT to return the current period from table T009B.
The function module needs value PERIV (Fiscal Year Variant) which is set in your customizing for your company code (table T001).
Table T009C is a good table as well showing the periods and their language relevant names should you need to show that as well.
data: lv_poper_l type poper,
lv_pgjahr_l type bdatj,
lv_date type sydatum,
lv_periv type periv.
* Set Posting date
lv_date = sy-datum.
* Determine Financial Period Variant
select single periv into lv_periv
from t001
where bukrs = pv_bukrs. "PV_BUKRS is the company code
if sy-subrc = 0.
* determine posting period
call function 'DATE_TO_PERIOD_CONVERT'
exporting
i_date = lv_date
i_periv = lv_periv
importing
e_buper = lv_poper_l "Contains period
e_gjahr = lv_pgjahr_l "Contains year
exceptions
input_false = 1
t009_notfound = 2
t009b_notfound = 3
others = 4.
endif.
