Restricted assets under US GAAP are typically reported on a company's balance sheet and represent funds that are limited in their use according to specific restrictions imposed by donors, grantors, or legal requirements. The calculation and accounting for restricted assets depend on the nature of the restriction.

1. Temporarily Restricted Assets: When assets are received with restrictions that will eventually be lifted (such as when a grant has specific project completion requirements), they are initially recorded at fair value in a separate net asset class called "temporarily restricted net assets." As the restrictions are fulfilled, the assets are reclassified into unrestricted net assets, and the associated restrictions are released to the statement of activities.

2. Permanently Restricted Assets: These are assets donated with restrictions that are permanent in nature, such as endowment funds. The fair value of the assets is recorded in a separate net asset class called "permanently restricted net assets." The income generated from these assets is typically used according to the donor's stipulations.

To calculate restricted assets, you would sum the values of all assets that have these restrictions applied to them. This can include cash, investments, property, equipment, or other resources. It's important to maintain clear records of the restrictions associated with each asset and track the changes in those restrictions over time.

The presentation and accounting for restricted assets are governed by ASC 958-605, Not-for-Profit Entities - Revenue Recognition. The not-for-profit entity should disclose information about its restricted assets in its financial statements, including the nature and purpose of the restrictions and how the restrictions are expected to be lifted.