I believe that 100% of Afro-Americans have Black Native American heritage. This results from the fact that the slaves on the plantations when Africans came to America were already Black Native Americans (BNA).
The BNA mated with the African slaves. The white racists to made sure they took the BNA lands often ignored the treaties they made with the BNA from New England down to Florida, by taking the BNA tribesmen captured after a War and enslaving them, while the BNA not enslaved was given the Bible, made Christian, and labled "free colored".
Over time, the freed African slaves were also forced to live in the "free colored" communities". In the "free colored" communities BNA and former African slaves mated. The "free colored" communities were often situated on choice real-estate, that whites took whenever they saw fit.
After the Revolutionary War, some BNA moved to Canada with the British. Some of the remaining BNA tribesmen were allowed to live as "free colored" people in places like Seneca Village (the location of today's Central Park), and Martha's Vinyard.
In places like Seneca Village and Martha's Vinyard, freed African slaves joined and mated with BNA. These "free colored" communities remained centers of Afro-American commerce and "citizenship", until whites took the land from the Afro-Americans. Today Martha's Vinyard and Central Park are frequented by white elites.
Due to the interactions between BNA and African slaves as " free colored" people and slaves on the plantation my guess is that 100% of Afro-Americans have BNA ancestry.