Calculate fiscal year in SQL Server

Building on the answer above by @csaba-toth, and assuming your fiscal year starts on the first day of the month

year(dateadd(month, (12 -FyStartMonth + 1), <date>)

My FY starts 1-July, the 7th month, so my constant is (12 - 7 + 1 =) 6.

Test cases (as of 25-Sep-2019):

select year(dateadd(month, 6, getdate()))
, year(dateadd(month,6, '1/1/2020'))
, year(dateadd(month, 6, '7/1/2020'))
, year(dateadd(month, 6, '6/30/2020'))

Returns:

2020    2020    2021    2020

I do believe this is the simplest and perhaps most comprehensible implementation.

DECLARE @DateFieldName DATETIME = '1/1/2020'

--UK Fiscal Year

SELECT 
CASE 
  WHEN MONTH(@DateFieldName) in (1,2,3)
   THEN CONCAT(YEAR(@DateFieldName) -1 , '-' , YEAR(@DateFieldName) )
   ELSE CONCAT(YEAR(@DateFieldName) , '-' , YEAR(@DateFieldName)+1 )  
  END AS [FISCAL YEAR]

--RESULT = '2019-2020'

For one year in the past and a start date of oct 1st 10-1-2021

Code:

CAST(CONVERT (varchar(4),YEAR(GetDate())-1) + '-' + '10' + '-' + '01' AS Datetime2(0))