The calculator shows how much GDP and tax revenue Britain would forgo if it leaves the European Union with no preferential trade deal.

EU negotiators may ask the UK to hand over as much as 100 billion euros (84 billion pounds) as part of an orderly departure from the trading bloc. Britain might be able to avoid this bill by leaving without a trade deal, but doing so would lower the UK’s future growth rate.

The main inputs are Britain’s future growth rate, the hit to annual growth from a chaotic exit, and the discount rate at which future output is converted into today’s money.

The growth rate is set to 1.8 percent, which is the average real growth rate forecast by the International Monetary Fund.

The discount rate is set at zero, because the growth forecasts are already adjusted for inflation. But you can use a higher figure if desired.

The calculator’s outputs are the cumulative GDP that Britain will forgo by 2030 in the event of a chaotic Brexit, and the amount of tax revenue it will lose assuming that the exchequer continues to collect a third of GDP.

For more interactive calculators and agenda-setting comment visit: BREAKINGVIEWS