Antidumping duties (ADD) are special tariffs imposed by a country's government on imported goods that are believed to be priced below fair market value—often at prices lower than those in the exporter's home market or even below the cost of production.

Why do anti-dumping duties exist?

Dumping occurs when a foreign exporter sells goods in another country's market at an unfairly low price. This practice can harm domestic industries by undercutting local competitors, leading to job losses and market distortions. To counteract this, governments investigate such cases and may impose extra duties (antidumping duties) on the imported products, raising their cost and leveling the playing field for domestic producers.

How are Dumping Duties Determined?

If a government agency (in the U.S., typically the Department of Commerce and U.S. International Trade Commission) finds evidence of dumping and determines it is harming domestic industry, it will calculate the margin of dumping (the difference between the export price and the normal value).
The additional duty applied is generally equal to this dumping margin.

Importers of products subject to antidumping duties must pay these extra tariffs on top of regular import duties, which can significantly increase the cost of importing affected goods.