A novel inbred maize variety designated PHB4D and seed, plants and plant parts thereof. Methods for producing a maize plant that comprise crossing inbred maize variety PHB4D with another maize plant. Methods for producing a maize plant containing in its genetic material one or more traits introgressed into PHB4D through backcross conversion and/or transformation, and to the maize seed, plant and plant part produced thereby. Hybrid maize seed, plant or plant part produced by crossing the inbred variety PHB4D or a trait conversion of PHB4D with another maize variety. Inbred maize varieties derived from inbred maize variety PHB4D, methods for producing other inbred maize varieties derived from inbred maize variety PHB4D and the inbred maize varieties and their parts derived by the use of those methods.