The ISO string format will always convert regardless of local settings.--*** Test Data ***CREATE TABLE #t( dob date NOT NULL);INSERT INTO #tVALUES ('19460413'), ('19470331');--*** End Test Data ***select * from #t;DECLARE @today date ='20150101';SELECT dob ,CASE WHEN DATEADD(year, DATEDIFF(year, dob, @today), dob) > @today THEN DATEDIFF(year, dob, @today) - 1 ELSE DATEDIFF(year, dob, @today) END AS AgeAsOf@todayFROM #t;