versions of iOS devices and Mac. Because the Company has neither VSOE nor TPE for the unspecified software upgrade rights or the non- software services, revenue is allocated to these rights and services based on the Company’s ESPs. Revenue allocated to the unspecified software upgrade rights and non-software services based on the Company’s ESPs is deferred and recognized on a straight-line basis over the estimated period the software upgrades and non-software services are expected to be provided for each of these devices, which ranges from two to four years. 

The Company’s process for determining ESPs involves management’s judgment and considers multiple factors that may vary over time depending upon the unique facts and circumstances related to each deliverable. Should future facts and circumstances change, the Company’s ESPs and the future rate of related amortization for software upgrades and non-software services related to future sales of these devices could change. Factors subject to change include the unspecified software upgrade rights offered, the estimated value of unspecified software upgrade rights, the estimated or actual costs incurred to provide non-software services and the estimated period software upgrades and non-software services are expected to be provided. 

The Company records reductions to revenue for estimated commitments related to price protection and other customer incentive programs. For transactions involving price protection, the Company recognizes revenue net of the estimated amount to be refunded, provided the refund amount can be reasonably and reliably estimated and the other conditions for revenue recognition have been met. The Company’s policy requires that, if refunds cannot be reliably estimated, revenue is not recognized until reliable estimates can be made or the price protection lapses. For the Company’s other customer incentive programs, the estimated cost is recognized at the later of the date at which the Company has sold the product or the date at which the program is offered. The Company also records reductions to revenue for expected future product returns based on the Company’s historical experience. Future market conditions and product transitions may require the Company to increase customer incentive programs that could result in reductions to future revenue. Additionally, certain customer incentive programs require management to estimate the number of customers who will actually redeem the incentive. Management’s estimates are based on historical experience and the specific terms and conditions of particular incentive programs. If a greater than estimated proportion of customers redeems such incentives, the Company would be required to record additional reductions to revenue, which would have an adverse impact on the Company’s results of operations. 

Valuation and Impairment of Marketable Securities 

The Company’s investments in available-for-sale securities are reported at fair value. Unrealized gains and losses related to changes in the fair value of securities are recognized in accumulated other comprehensive income, net of tax, in the Company’s Consolidated Balance Sheets. Changes in