The purpose of this paper is to compare classical handbook methods used to predict performance parameters such as range and endurance to computer based methods. Three different methods are compared: classical handbook methods are based on simple drag polars and engine performance data, spreadsheet methods use more detailed engine data and drag polars and third is the use of APP (Aircraft Performance Program), a commercially available software program. The advantages and disadvantages of each method are described and accuracy listed based on existing airplanes. One example is used: a business jet type aircraft. Methods used are described and inputs and outputs of the different programs used are shown.