A good number of countries don't follow calendar year as the financial year. For example, India's financial year start is 1-Apr and finishes on 31-Mar. Hence, currently (20-Feb-16), the financial year is 2015-16 (It is also written as FY16). On 1-Apr-16, it will become 2016-17 (It is also written as FY17).
Now if a date is given, then following formula can be used to derive 2015-16 kind of result.
=YEAR(A1)-(MONTH(A1)<=3)&"-"&YEAR(A1)+(MONTH(A1)>3)
To generate FY16 kind of result, following formula can be used
="FY"&RIGHT(YEAR(A1)+(MONTH(A1)>3),2)