The U.S. debt ceiling is a statutory limit set by Congress on the amount of national debt that the federal government is allowed to incur. When the government approaches the debt ceiling, it must either seek an increase in the limit from Congress or take measures to reduce its borrowing.

In the past, the U.S. has come close to breaching the debt ceiling on several occasions, and in some cases, the government has temporarily suspended the limit or taken other measures to avoid default.

The US has failed to pay debt obligations on time on several occasions. This Reason article describes five cases which could be characterized as default, and this Congressional Research Service (CRS) report explores three of them in more detail. The most recent occurrence was the 1979 "mini-default", when a technical error led to the late payment to holders of Treasury securities. CRS says the following about the overall record of US debt repayment:

The historical record appears not to support the contention that the U.S. government has had an unblemished payment record since its origin. Under any reasonable definition of default, the federal government defaulted in 1814. The Treasury Secretary of the time, Alexander Dallas, referred to “every sort of embarrassment.” The current website of the U.S. Treasury notes that Secretary Dallas faced a “bankrupt” Treasury. The failure of the Treasury to pay interest on its securities due to Boston banks in 1814 represents an unambiguous default event.

Regarding the 1979 "mini-default" CRS says:

Claims that payment delays to small investors holding Treasury securities in the spring of 1979 constituted a default or a “technical default” appear weaker. Delays affected only a relatively small proportion of Treasury securities and the federal government responded to mitigate the inconvenience suffered by those investors. The legal document setting out terms for Treasury securities contained no default clause.

According to Reuters, the deadline for a debt ceiling increase could come earlier than expected:

The U.S. government's deadline to raise the $31.4 trillion debt ceiling could be sooner than expected, raising the prospect of a short-term debt limit extension, analysts said on Tuesday.

Goldman Sachs analysts said weak tax collections so far in April indicate a higher probability that the so-called "X-date," when the government is no longer able to pay all its bills, would be reached in the first half of June. Analysts at Citi said they expected a short-term deal in June or July.

The Treasury Department has warned that the federal government could reach the moment when it will no longer be able to meet its financial obligations as early as June 5, while the nonpartisan Congressional Budget Office has forecast that moment would come sometime between July and September.