foreign earnings that we consider indefinitely reinvested outside the United States could materially impact our income tax provision and effective tax rate.

We record a valuation allowance to reduce our deferred tax assets to the amount that is more likely than not to be realized. In order for us to realize our deferred tax assets, we must be able to generate sufficient taxable income in those jurisdictions where the deferred tax assets are located. We consider future growth, forecasted earnings, future taxable income, the mix of earnings in the jurisdictions in which we operate, historical earnings, taxable income in prior years, if carryback is permitted under the law and prudent and feasible tax planning strategies in determining the need for a valuation allowance. In the event we were to determine that we would not be able to realize all or part of our net deferred tax assets in the future, an adjustment to the deferred tax assets valuation allowance would be charged to earnings in the period in which we make such a determination, or goodwill would be adjusted at our final determination of the valuation allowance related to an acquisition within the measurement period. If we later determine that it is more likely than not that the net deferred tax assets would be realized, we would reverse the applicable portion of the previously provided valuation allowance as an adjustment to earnings at such time.

We calculate our current and deferred tax provision based on estimates and assumptions that could differ from the actual results reflected in income tax returns filed during the subsequent year. Adjustments based on filed returns are generally recorded in the period when the tax returns are filed and the global tax implications are known, which can materially impact our effective tax rate.

The amount of income tax we pay is subject to ongoing audits by federal, state and foreign tax authorities, which often result in proposed assessments. Our estimate of the potential outcome for any uncertain tax issue is highly judgmental. A description of our accounting policies associated with tax related contingencies assumed as a part of a business combination is provided under “Business Combinations” above. For those tax related contingencies that are not a part of a business combination, we account for these uncertain tax issues pursuant to ASC 740, Income Taxes , which contains a two-step approach to recognizing and measuring uncertain tax positions taken or expected to be taken in a tax return. The first step is to determine if the weight of available evidence indicates that it is more likely than not that the tax position will be sustained in an audit, including resolution of any related appeals or litigation processes. The second step is to measure the tax benefit as the largest amount that is more than 50% likely to be realized upon ultimate settlement. Although we believe we have adequately reserved for our uncertain tax positions, no assurance can be given with respect to the final outcome of these matters. We adjust reserves for our uncertain tax positions due to changing facts and circumstances, such as the closing of a tax audit,