This Sunday the United States' statutory debt limit will once again go into effect, essentially reinstating the debt ceiling at the level of the U.S. debt on Sunday, probably around $18 trillion.
The reason the debt limit is returning to haunt our fiscal dreams is because Congress kicked the can down the road when it passed a suspension of the debt limit in February, 2014.
But it's hard to know how long the Department of Treasury can use "extraordinary measures" to keep paying its bills before it begins to risk defaulting on its debt. That's because government revenues are lumpy — lots comes in during tax season, for example. The best estimate sets the new deadline at some time in October or November.