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If the lease buy out as stated in the contract is approximately equal to the market value of the equipment (estimated) you should capitalize and depreciate the vans. However, if your clients have no interest in electing the buy out then simply expense the lease payments. Should they subsequently change their minds it will not matter since the expense, over time, will be the same. The advantage of capitalizing and depreciating the vans is that the depreciation method selection process can provide greater expense in the early years. If you are expensing the lease payments and the client elects to purchase the vans, the basis will be the purchase option price paid and you will then depreciate that.
If you capitalize how do you determine the split between interest and principal on the monthly payments?