Following his work on the D.C. survey, Banneker devoted his time to calculating astronomical data for his almanac, which would include tide tables, eclipses, and other useful information for farmers and the general public.

Banneker published annual almanacs for the years 1792 through 1797. These almanacs, published in multiple states, contained his own astronomical calculations and essays against slavery, establishing his reputation as an intellectual figure and abolitionist.

Banneker wrote a letter to then-Secretary of State Thomas Jefferson, challenging his views on racial equality and urging him to reconsider his stance on slavery. He included a copy of his almanac as evidence of African Americans' intellectual capabilities.

Jefferson replied to Banneker's letter, acknowledging his talent and expressing his hope that Banneker's achievements would help to dispel prejudices against African Americans. Jefferson also sent a copy of Banneker's almanac to the Academy of Sciences in Paris.

Banneker's almanacs brought him widespread recognition and became important tools for abolitionists. They provided tangible proof of African American intellectual ability and challenged the prevailing racist ideologies of the time.