From their FAQ, "...a proficient native speaker will know some 40,000 words of the list (i.e., 67%) ... [for second language speakers] our estimates range from

From their FAQ, "...a proficient native speaker will know some 40,000 words of the list (i.e., 67%) ... [for second language speakers] our estimates range from 6,000 words (10%) for a medium proficiency speaker to 20,000 words (33%) for a high-proficiency speaker." So well above their estimates, but they don't extrapolate on the source of those numbers - they might be available somewhere at http://crr.ugent.be http://crr.ugent.be