Why does the US government shut down, and what happens when it does?

The US government shuts down when Congress and the president have not agreed on funding before the new fiscal year starts on 1 October. Officially it is called a lapse in appropriations. The money to run federal agencies has to be approved by law each year, and without a new law, or a stopgap, agencies are not allowed to spend.

A federal law from 1870, the Antideficiency Act, bars officials from spending beyond what Congress has appropriated. It was not until 1980 that the Department of Justice issued legal opinions reading the act as requiring shutdowns during funding lapses, and since 1990 every funding gap lasting more than a few hours has produced one. As of November 2025, 11 funding gaps had led to furloughs.

Shutdowns tend to occur when there is a disagreement over budget allocations before the existing funding runs out. A continuing resolution can postpone one by extending funding for a set period while talks continue. But in the Senate, spending bills can be filibustered, so ending debate needs three-fifths of senators, which means one side often cannot pass a bill alone.

During a shutdown, agencies stop non-essential work, non-essential staff are furloughed, and only employees protecting human life or property keep working. The source lists a 43-day shutdown that began on 1 October 2025 among the most significant ones, alongside the 35 days of 2018-2019. Each side usually says the other caused it, and this lesson reports only how the mechanism works.