Cost overrun

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Cost overrun is defined as excess of actual cost over budget. Cost overrun is also sometimes called "cost escalation," "cost increase," or "budget overrun."

Cost overrun is common in infrastructure, building, and technology projects. One of the most comprehensive studies [1] of cost overrun that exists found that 9 out of 10 projects had overrun, overruns of 50 to 100 percent were common, overrun was found in each of 20 nations and five continents covered by the study, and overrun had been constant for the 70 years for which data were available. For IT projects an industry study by the Standish Group (2004) found that average cost overrun was 43 percent, 71 percent of projects were over budget, over time, and under scope, and total waste was estimated at US$55 billion per year in the US alone.

Spectacular examples of cost overrun are the Suez Canal with 1,900 percent, the Sydney Opera House with 1,400 percent, and the Concorde supersonic aeroplane with 1,100 percent. The cost overrun of Boston's Big Dig was 275 percent, or US$11 billion. The cost overrun for the Channel tunnel between the UK and France was 80 percent for construction costs and 140 percent for financing costs.

Three types of explanation of cost overrun exist: technical, psychological, and political-economic. Technical explanations account for cost overrun in terms of imperfect forecasting techniques, inadequate data, etc. Psychological explanations account for overrun in terms of optimism bias with forecasters. Finally, political-economic explanations see overrun as the result of strategic misrepresentation of budgets.

Cost overrun is typically calculated in one of two ways. Either as a percentage, namely actual cost minus budgeted cost, in percent of budgeted cost. Or as a ratio, viz. actual cost divided by budgeted cost. For example, if the budget for building a new bridge was $100 million and the actual cost was $150 million then the cost overrun may be expressed as 50 percent or by the ratio 1.5.