> This paper examines the impact of the UK's decision to leave the European Union (Brexit) in 2016. Using almost a decade of data since the referendum, we combine simulations based on macro data with estimates derived from micro data collected through our Decision Maker Panel survey. These estimates suggest that by 2025, Brexit had reduced UK GDP by 6% to 8%, with the impact accumulating gradually over time. We estimate that investment was reduced by between 12% and 18%, employment by 3% to 4% and productivity by 3% to 4%. These large negative impacts reflect a combination of elevated uncertainty, reduced demand, diverted management time, and increased misallocation of resources from a protracted Brexit process. Comparing these with contemporary forecasts – providing a rare macro example to complement the burgeoning micro-literature of social science predictions – shows that these forecasts were accurate over a 5-year horizon, but they underestimated the impact over a decade.