The US GAAP model for accounting for income taxes requires companies to record deferred taxes as compensation cost is recognized, as long as that particular type of instrument ordinarily would result in a future tax deduction. The measurement of the deferred tax asset is based on the amount of compensation cost recognized for book purposes. Changes in the stock price do not impact the deferred tax asset or result in any adjustments prior to settlement or expiration.

Upon settlement or expiration, excess tax benefits and tax deficiencies (the difference between the recorded deferred tax asset and the tax benefit of the actual tax deduction) are recognized within income tax expense.

The measurement of the deferred tax asset in each period is based on an estimate of the future tax deduction, if any, for the award measured at the end of each reporting period (based on the current stock price if the tax deduction is based on the future stock price).

When the expected tax benefits from equity awards exceed the recorded cumulative recognized expense multiplied by the tax rate, the tax benefit up to the amount of the tax effect of the cumulative book compensation expense is recorded in the income statement; the excess is recorded in equity.

When the expected tax benefit is less than the tax effect of the cumulative amount of recognized expense, the entire tax benefit is recorded in the income statement.