There are many different ways to depreciate property.  The simplest is the "straight line" method.  First, determine the "useful life" of the asset.  A computer may have a useful life of only five years, while a building may have a useful life of decades.  Second, deduct the "salvage value", or anticipated amount for which the asset can be sold at the end of its useful life, to obtain the depreciable basis.  (For real property, you would subtract the value of the land to arrive at the depreciable basis.)  Divide the depreciable basis by the number of periods (either months or years) over which the item will be depreciated.  The result is the depreciation expense for the asset per period.