Deferred tax assets are measured under ASC 740 at the enacted tax rates expected to apply when they are used. A company must record a valuation allowance against any portion it considers more likely than not to go unused, weighing evidence such as recent losses, the expiry dates of carryforwards, and expected future taxable income. Since ASU 2015-17, deferred tax balances are classified as noncurrent, so for most companies today the whole net deferred tax asset sits in this line.
Within a single tax jurisdiction a company offsets its deferred tax assets and liabilities and shows one figure, so a balance-sheet deferred tax asset is net of liabilities in the same jurisdiction. In XBRL filings the netted noncurrent figure is tagged DeferredIncomeTaxAssetsNet or DeferredTaxAssetsNetNoncurrent, and the valuation allowance disclosed in the tax footnote is tagged DeferredTaxAssetsValuationAllowance. The footnote also shows the gross components, such as operating loss carryforwards and accrued expenses.
The value of a deferred tax asset depends entirely on the company earning enough taxable income to use it. Large assets supported mainly by loss carryforwards are only as good as the company's prospects for future profits. Changes in the valuation allowance can move reported earnings sharply: releasing an allowance creates a one-time tax benefit, while establishing one creates a large tax charge. Analysts often exclude deferred tax assets from tangible or conservative measures of book value, especially at companies with a history of losses.