Capitalization rate (or 'Cap Rate') is a real estate valuation measure used to compare different real estate investments. Although there are many variations, a cap rate is often calculated as the ratio between the net operating income produced by an asset and the original capital cost (the price paid to buy the asset) or alternatively its current market value. Capitalization rate (or 'Cap Rate') is a real estate valuation measure used to compare different real estate investments. Although there are many variations, a cap rate is often calculated as the ratio between the net operating income produced by an asset and the original capital cost (the price paid to buy the asset) or alternatively its current market value.