It is hard to calculate the current cost of Brexit, because there is no obvious counterfactual. This column calculates the cost by letting a matching algorithm determine which combination of comparison economies best resembles the pre-referendum growth path of the UK economy. The difference in output between the UK economy and its synthetic doppelganger adds up to a loss of 1.3% of GDP, or close to £300 million per week, since the vote took place. This implies a cumulative cost of more than £60 billion by the end of 2018.