A spreadsheet model is a system of calculations and numbers in a spreadsheet program (eg. Microsoft Excel) that is intended to simulate a real-world situation. Spreadsheet models consist of a user control input value (or set of values) which then are passed through a series of calculations to produce an output value (or set of output values). Spreadsheet models can also take into consideration fixed amounts (eg. employee wages per month) and variable amounts (number of items sold). Spreadsheet models are common in business planning and forecasting.