President Donald Trump introduced his “discounted reciprocal tariffs” on over 200 countries on April 2. Most countries receive a base tariff rate of 10%, but for countries receiving more, the rates were calculated by halving a rate he displayed as “tariffs charged to the U.S.A. including currency manipulation and trade barriers.”

The Trump administration took that formula’s figure, -0.5 for South Korea, and divided it by two to calculate the U.S. “discounted reciprocal” tariff rate. So, while South Korea imposes an effective tariff rate of .79 percent on U.S. goods, the reciprocal tariff rate the U.S. is imposing on South Korea is 25 percent.

The administration appears to have used a simple, two-step formula to calculate the "reciprocal tariffs" applied to trading partners.

President Donald Trump's "reciprocal" tariffs against trading partners raise import taxes on friends, foes, and uninhabited islands, leaving trade experts guessing the strategy behind them.

But if the tariffs calculations have been hastily put together by an AI, that would indicate a new depth of incompetence for the Trump administration, closely following that of using Signal chat to plan military operations and including a journalist in that same chat.

The formula used by the Trump administration to calculate 'Liberation Day' reciprocal tariffs is based on trade deficits.

Some overseas officials challenged Trump's math, such as George Plant, the administrator of Norfolk Island, who told the Guardian that "there are no known exports from Norfolk Island to the United States and no tariffs or known non-tariff trade barriers on goods coming to Norfolk Island."

Economist Wojtek Kopczuk asked ChatGPT to calculate tariffs to balance out the U.S. trade deficit. He received a similar answer to the White House’s documentation, showing the AI used “a basic approach” that divided the trade deficit by the total trade. Entrepreneur Amy Hoy ran a similar experiment, yielding identical results from AI models.

Complex formulas and stacked duty rates—how companies calculate what to pay.