US can only pay its bills until March, Treasury Secretary Jack Lew warns But Mr Lew said the department would exhaust these so-called extraordinary measures sometime between late February and early March. After then, it would no longer be able to borrow to cover its expenses. "While this forecast is subject to inherent variability, we do not foresee any reasonable scenario in which the extraordinary measures would last for an extended period of time," Mr Lew said. Once it loses the ability to borrow, Treasury would pay its bills by relying on incoming revenue and any cash left in public coffers. After the money runs out, the government could start missing payments on its debt and other obligations, such as Social Security pensions. Many economists think a US default could trigger a financial panic and perhaps even an economic depression. Heated debates in Washington over the debt ceiling have periodically roiled financial markets since 2011, when the risk of default helped prompt Standard & Poor's to downgrade America's debt rating. Political dysfunction again rattled Wall Street in October. In November, the Congressional Budget Office estimated the Treasury might be able to stave off defaulting on obligations next year until as late as June, depending on the strength of tax receipts. Some private sector analysts have also said the government could stretch its cash until around then. But the Treasury is holding firm that borrowing authority will expire no later than early March. A senior official said the Treasury's cash flow estimates for next year include the possibility that government revenues might be boosted by higher revenues due to faster economic growth or dividend payments from housing finance firms that are controlled by the government.