SELECT DATEADD(qq, DATEDIFF(qq, 0, GETDATE()), 0)
SELECT DATEADD (dd, -1, DATEADD(qq, DATEDIFF(qq, 0, GETDATE()) +1, 0))
And from quarter and year variables:
DECLARE @MyYear INT = 2021;
DECLARE @MyQuarter INT = 1;
DECLARE @MyDate DATE;
-- Get date from quarter and year
SET @MyDate = DATEADD(qq, @MyQuarter - 1, DATEFROMPARTS(@MyYear, 1, 1))
SELECT @MyDate
-- Last day of Quarter
SELECT DATEADD(dd, -1, DATEADD(qq, DATEDIFF(qq, 0, @MyDate) +1, 0))