British Prime Minister Boris Johnson shakes hands with US President Donald Trump onstage during the annual NATO heads of government summit on December 4, 2019 in Watford, England.

The U.S. and the U.K. are starting trade talks later this month amid skepticism that any deal won't bring the massive economic boon that is being predicted.

The agreement could increase U.K. growth by 0.16% by the year 2035 in a best-case scenario — about $3.4 billion ($4.35 billion) — according to a report published by the U.K.'s international trade department. The same document also estimated that the deal could grow the U.S. economy by between 0.03% and 0.05% over the same 15-year period.

Ahead of their upcoming talks, both countries have outlined their main objectives as they look to reach a final agreement by the end of the year.