The Congressional Budget Office said the war in Iran cost the United States roughly $38 billion through Aug. 1 and significantly depleted U.S. munitions, in a 19-page analysis limited because the Defense Department did not respond to requests for information. The C.B.O. projected the war would continue to cost approximately $2 billion to $3 billion per month, and rebuilding depleted U.S. stockpiles could take "at least five years."

The cost assessment "reflects the costs of replacing expended munitions and equipment lost in battle, increased flying hours, other operations and increased fuel costs," the office said. It is roughly in line with congressional testimony delivered in late July by Defense Secretary Pete Hegseth, who estimated then that the war had cost $37.5 billion. The analysis came at the request of top Democrats, including Representative Brendan Boyle of Pennsylvania, the top Democrat on the Budget Committee.

Because the Pentagon declined to provide any information, the budget office said it relied on government databases and public reports. It did not include costs that "could emerge in the future" or the costs of repairing damaged military bases. The office said the main opportunity cost has been "the large expenditure of missile defense interceptors," leaving a reduced inventory for several years.

The White House has asked Congress for as much as $70 billion in emergency military spending, but the request has languished on Capitol Hill.