The National Day of Reason is an unofficial secular celebration for humanists, atheists, and other secularists and freethinkers in response to the official National Day of Prayer of the United States.^[1][2] The day is celebrated on the first Thursday in May of every year, to coincide with the National Day of Prayer.

The National Day of Reason was created by the American Humanist Association and the Washington Area Secular Humanists in 2003.^[3] In addition to serving as a holiday for secularists, the National Day of Reason was created in response to the perceived unconstitutionality of the National Day of Prayer. According to the organizers of the National Day of Reason, the National Day of Prayer, "violates the First Amendment of the United States Constitution because it asks federal, state, and local government entities to set aside tax dollar supported time and space to engage in religious ceremonies".^[4]