Patrick Bisciari published an overview of existing studies on the effects of Brexit from experts at institutions such as the London School of Economics, the IMF and the Catholic University of Leuven (KUL). He then took the median value of the impact predicted by all the studies.
With the exception of Ireland and Luxembourg, Belgium with be the EU 27 country that is hit the hardest by Brexit. This is the case whether or not the UK leaves with under the terms of a Brexit agreement. However, Mr Bisciari concludes that the difference in the level of impact between Belgium and the two countries that will be hardest hit is quite large.
The impact on Belgium is more comparable to that on Cyprus or The Netherlands.
Nevertheless, the IMF predicts a loss of 0.9% of GDP for Belgium as a result of a no deal Brexit. This is only slightly higher than the predicted average impact on GDP for the EU as a whole.
Not surprisingly, the negative impact will be greatest on the UK economy.