The US government under President Donald Trump used a straightforward formula to calculate tariffs charged to the US, sparking confusion among trade economists at first. The methodology was later revealed to be simple: take each country’s trade deficit with the US, divide it by the value of its exports to the US, and then halve it.
Using Vietnam as an example, the Trump administration claimed Vietnam imposed a 90% tariff on US goods, which would result in a reciprocal 46% tariff. However, according to official US data, Vietnam exported $136.6 billion worth of goods to the US but imported only $13.1 billion. This resulted in a trade surplus of $123.5 billion with the US.
When calculating the “reciprocal” tariff, the formula gave Vietnam a 90% tariff, which Trump allegedly reduced by nearly half, resulting in a 46% tariff for Vietnam. The White House repeated this methodology for all countries on its tariff chart, punishing them for having trade surpluses with the US rather than imposing tariffs themselves.
Source: https://edition.cnn.com/politics/live-news/trump-tariffs-news-04-03-25/index.html