Generally, the priority date is the date when the immigrant petition is properly filed with U.S. Citizenship and Immigration Services (USCIS). In some instances, the priority date is when the labor certification application was accepted for processing by the Department of Labor.
Congress sets limits on the number of immigrant visas that can be issued each year. In order for a visa interview to be scheduled, an immigrant visa must be available. The Department of State publishes a monthly Visa Bulletin which lists the cut-off dates that govern visa availability. Applicants who have a priority date earlier than the cut-off date published in the most current Visa Bulletin are eligible to apply for a visa.
The cut-off dates on the Department of State Visa Bulletin are adjusted monthly and are posted on travel.state.gov