I have a basic query:
SELECT dtCreated , bActive , dtLastPaymentAttempt , dtLastUpdated , dtLastVisit FROM Customers WHERE (bActive = \'true\
As @Forte L. mentioned you can do the following as well;
SELECT dtCreated , bActive , dtLastPaymentAttempt , dtLastUpdated , dtLastVisit , DATEDIFF(day, dtCreated, dtLastUpdated) Difference FROM Customers WHERE (bActive = 'true') AND (dtLastUpdated > CONVERT(DATETIME, '2012-01-0100:00:00', 102))