Exponential‐growth bias (EGB) is the tendency for individuals to partially neglect compounding of exponential growth. We develop a model wherein biased agents misperceive the intertemporal budget constraint, and derive conditions for overconsumption and dynamic inconsistency. We construct an incentivized measure of EGB in a US‐representative population and find substantial bias, with approximately one third of subjects estimated as the fully biased type. The magnitude of the bias is negatively associated with asset accumulation, and does not respond to a simple graphical intervention.