The provision for income taxes for interim tax periods is generally determined using an estimate of the Company’s annual effective tax rate, excluding jurisdictions for which no tax benefit can be recognized due to valuation allowances, and adjusted for discrete tax items in the period. Each quarter the Company updates its estimate of the annual effective tax rate and makes a cumulative adjustment if the estimated annual tax rate has changed.

 The Company’s effective tax rate generally differs from the U.S. federal statutory tax rate primarily due to a valuation allowance related to the Company’s U.S. federal and state deferred tax assets partially offset by the windfall from share-based compensation tax deductions.