When are patent applications published by the USPTO?

Patent applications are generally published by the USPTO 18 months after the earliest filing date for which a benefit is sought. This is specified in 35 U.S.C. 122(b)(1)(A):

Subject to paragraph (2), each application for a patent shall be published, in accordance with procedures determined by the Director, promptly after the expiration of a period of 18 months from the earliest filing date for which a benefit is sought under this title. At the request of the applicant, an application may be published earlier than the end of such 18-month period.

There are some exceptions to this rule, such as applications that are no longer pending or are subject to a secrecy order. Applicants can also request early publication or non-publication under certain conditions.