The sum of depreciation from lease inception to date. It is a negative number, to indicate a credit. If the lease has an ownership transfer or reasonably certain purchase option, the depreciable life is the economic life; otherwise, it is the lease term.
For finance leases, depreciation is calculated based on the depreciation method selected. For an ASC 842 operating lease, accumulated depreciation is the sum of liability paid, minus prepaid rent (if the lease is in the middle of a payment period), plus the difference between level and cash rent, plus amortization of initial direct costs and lease incentives, if any.