A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
In C2:
=SWITCH(LEFT(B2, 2),
"AA", IF(DAY(TODAY())<16, DATE(YEAR(TODAY()), MONTH(TODAY()), 15), EOMONTH(TODAY(), 0)),
"BB", EOMONTH(TODAY(), 0),
"CC", EOMONTH(TODAY(), 5-MOD(MONTH(TODAY())+4, 6)),
"DD", EOMONTH(TODAY(), 2-MOD(MONTH(TODAY()), 3)),
"EE", EOMONTH(TODAY(), 2-MOD(MONTH(TODAY())-1, 3)))