From the Document: "When a new session of Congress begins in January, one of its first orders of business is to receive the annual budget submission of the President. Following receipt of the President's budget, Congress begins consideration of the budget resolution and other budgetary legislation for the upcoming fiscal year, which starts on October 1. The transition from one presidential administration to another raises special issues regarding the annual budget submission. Which President--the outgoing President or the incoming one--is required to submit the budget, and how will the transition affect the timing and form of the submission? The purpose of this report is to provide background information that addresses these questions."
CRS Report for Congress, RS20752
Congressional Research Service: https://crsreports.congress.gov/