AX / Dynamics 365 For Finance and Operations blog

SELECT
DATEADD(yy, DATEDIFF(yy, 0, GETDATE()), 0) AS StartOfYear,
DATEADD(yy, DATEDIFF(yy, 0, GETDATE()) + 1, -1) AS EndOfYear

The above query gives a datetime value for midnight at the beginning of December 31. This is about 24 hours short of the last moment of the year. If you want to include time that might occur on December 31, then you should compare to the first of the next year, with a < comparison. Or you can compare to the last few milliseconds of the current year, but this still leaves a gap if you are using something other than DATETIME (such as DATETIME2):

SELECT
DATEADD(yy, DATEDIFF(yy, 0, GETDATE()), 0) AS StartOfYear,
DATEADD(yy, DATEDIFF(yy, 0, GETDATE()) + 1, -1) AS LastDayOfYear,
DATEADD(yy, DATEDIFF(yy, 0, GETDATE()) + 1, 0) AS FirstOfNextYear,
DATEADD(ms, -3, DATEADD(yy, DATEDIFF(yy, 0, GETDATE()) + 1, 0)) AS LastTimeOfYear

Other Periods

This approach has two nice aspects: good performance and it can easily be changed for other periods by replacing both occurrences of yy (=year) with a different string:

yy, yyyy year
qq, q quarter
mm, m month
wk, ww week