A deferred tax asset can arise from differences in recognition of income. In this thread we're talking about the deferred tax asset arise from unearned income.
For instance, a financial company is a lessor and receives advance mortgage payments for a building it leases, the tax and book accounting purposes of the payments may differ. The tax laws, under certain circumstances, require the financial company to take into income the entire amount of the payment, even though the payments include monthly payments for the period occurring after the close of the tax year.
For book purposes, this income is not included into income until the payment is actually "earned," that is to say, as each month passes. This is also a deferred tax asset because the item causes a greater amount of income in the current period for tax purposes than it does for book purposes. Why? Because in subsequent years, the corporation will recognize book income when there is not a corresponding recognition of taxable income. Thus, where income is recognized in the current year for tax purposes and will be recognized in subsequent years for book purposes, a deferred tax asset arises.