In addition to every Sunday, the days to be observed as holy days of obligation in the Latin rite arch/dioceses of the United States of America include the following solemnities: Mary, Mother of God (January 1); the Ascension of the Lord (Forty Days after Easter); the Assumption of the Blessed Virgin Mary (August 15); All Saints (November 1); Nativity of the Lord [Christmas] (December 25). 

Whenever January 1, the solemnity of Mary, the Mother of God; or August 15, the solemnity of the Assumption of the Blessed Virgin; or November 1, the solemnity of All Saints falls on a Saturday or on a Monday, the obligation to attend Mass is lifted. The faithful, however, are encouraged to attend Mass on those days.