It's all about the detail and to how far Trump and May want to go.
"I don't expect a detailed discussion tomorrow. It's about deciding whether or not the U.K. and the U.S. want a trade deal and when," Andre Sapir, senior fellow at Bruegel, told CNBC on Thursday.
He added, that usually, the smaller economy, in this case the U.K., has more to gain with a trade deal.
But a free trade deal between both countries could be more about political symbolism than anything else and thus easier to conclude.
"(A trade deal) will help President Trump to stave off some criticism that he is anti-trade," CER's Korteweg said. "It works very nicely for Prime Minister May too because she can show there's life outside the EU," he added.
Both countries already enjoy significant deep trade ties. In fact, in 2015, the U.K. ran a trade surplus in goods and services with the U.S. However, they could still lower some of the remaining tariffs or indeed opening up other sectors, such as health care and agriculture, which could be controversial and time costly.