The Treasury Department says it could start defaulting on U.S. obligations after Oct. 17. Other estimates suggest it could be weeks until the U.S. reaches that point. Key dates that investors and policy makers are watching:

Oct. 17

What happens: The U.S. will exhaust emergency measures it has used since reaching the $16.7 trillion debt limit in May. By this date, it expects to have only $30 billion of cash and any incoming tax revenue to pay obligations. Early that afternoon, the government rolls over, or replaces, $120 billion in maturing debt.

Why it matters: Missing the publicly established deadline could rattle investors and diminish the appetite for some debt, as the potential for a default draws nearer.