US military operations against Iran could strain the Pentagon’s operating budget and affect its ability to conduct future operations, according to the Washington DC-based think tank Center for Strategic and International Studies (CSIS).The think tank has estimated the cost of the operations at between $34 billion and $42 billion. Although the fighting appears to be winding down, Congress now faces the challenge of covering these expenses, as neither the 2026 nor the 2027 defence budgets have factored in these additional costs, according to the report.Since the operations were not budgeted for, the US Congress must either approve supplemental appropriations or reprogramme existing funds. Supplemental appropriations would be preferred by the Pentagon to avoid undermining modernisation programmes, the report said. However, timing remains a critical factor, as fiscal year 2027 funds will not be available before October 2026.The war unfolded in distinct phases, beginning with deployment, which cost only $170 million, followed by a brief but intense combat phase dominated by expensive long-range missile strikes. Once air superiority was established after the destruction of air defences, US forces relied more heavily on cheaper short-range munitions such as JDAM smart bombs.The Department of Defense’s largest expense was munitions, totalling $26.1 billion, with more than 13,600 strike weapons fired, including Tomahawk missiles and Joint Air-to-Surface Standoff Missiles (JASSM). Regional partners also helped reduce costs by intercepting many Iranian drones and missiles headed towards US bases.Operational tempo added $750 million in incremental costs due to extended deployments, as well as hazard pay for US service members who took part in the operations. Equipment losses ranged between $1.8 billion and $3.5 billion, with 42 aircraft lost or damaged, most of them drones.Damage to bases was also significant, with estimates ranging between $4 billion and $9.4 billion, as Iranian strikes targeted barracks, hangars and warehouses. Rising fuel prices added another $1.4 billion, while miscellaneous costs, including security enhancements, contributed $100 million.Beyond the Pentagon, other federal agencies absorbed about $1 billion in costs, covering cyber defence, embassy security and nuclear monitoring. Veterans’ benefits are projected to add $400 million annually, amounting to $12 billion over three decades, according to the report.The broader economic impact was far greater, with Moody’s estimating the cost at $132 billion, largely due to fuel price hikes. Higher fuel prices alone cost US consumers $40 billion.Other institutions have produced varying estimates for the cost of the conflict. The Department of Defense initially cited $25 billion to $29 billion, excluding damage to bases. The American Enterprise Institute estimated the cost at between $31 billion and $41 billion, broadly consistent with CSIS. Brown University’s estimate was higher as it factored in the $40 billion fuel cost to the wider US economy.The Pentagon’s supplemental request of $80 billion also included unrelated modernisation expenses, inflating the overall figure.