Bent Flyvbjerg

Overview

Bent Flyvbjerg is a Danish researcher who is widely described as the world's leading expert on why large construction projects go over budget. He is a professor emeritus at the University of Oxford's Saïd Business School and a professor at the IT University of Copenhagen. His interest began in the 1990s with a bridge and tunnel project in his home country, the Great Belt Bridge, whose costs ran far past officials' estimates. Flyvbjerg began collecting data on big projects around the world, and over decades his team built a database of more than 16,000 projects from 136 countries, the largest of its kind. The data revealed what he calls the iron law of megaprojects: over budget, over time, under benefits, over and over again. In 2003, he helped develop a method called reference class forecasting, which predicts a new project's cost by looking at how similar past projects actually turned out, and he explained his findings for a general audience in the 2023 bestseller How Big Things Get Done, written with Dan Gardner.

Why He Matters

Bent Flyvbjerg's work matters because it proves, with data, that estimating is hard and that getting it right is rare. His research shows that only about half of large projects finish on budget, and that costs balloon for predictable reasons, including optimism, pressure to make a project look affordable, and the simple fact that big projects run into surprises. His answer is not to guess harder but to look at the track record of similar projects, which is exactly what a good estimator does with historical cost data. For young people, his career shows that a construction career can be about ideas as well as buildings, and that asking a stubborn question- why do estimates keep failing- can reshape how governments and companies around the world plan the things they build.