I'm hoping someone here can clarify what Etihad means by a 'rolling year' when accruing miles to upgrade to a higher tier. Basically, I flew with Etihad on 10 June 2014 and am trying to complete travel before then to qualify for gold. Does the 'rolling year' refer to calendar months, meaning I need to complete travel before the month of June, or does it go by the actual date of anniversary?

thanks in advance.