An haife shi a Seattle, Washington, a ranar 28 ga Oktoba, 1955. Shi ne dan William H. Gates Sr. (haifaffen 1925) da Mary Maxwell Gates (1929<unk>1994). Kakanninsa sun hada da Ingilishi, Jamusanci, Irish, da Scots-Irish. Mahaifinsa sanannen lauya ne, kuma mahaifiyarsa ta yi aiki a kwamitin gudanarwa na First Interstate BancSystem da United Way. Mahaifin mahaifiyar Gates shi ne J. W. Maxwell, shugaban bankin kasa. Gates yana da 'yar'uwa daya, Kristi (Kristianne), da' yar'uwa, Libby. Shi ne na huɗu na sunansa a cikin iyalinsa, amma an san shi da William Gates III ko "Trey" saboda mahaifinsa yana da "II" mai kyau.
zai ko da yaushe aiwatar da software code daidai