Seat belt fit relative to the occupant’s anatomy affects kinematics and may affect injury risk in crashes. Recent studies have shown that belt routing for drivers is significantly associated with occupant characteristics, particularly body mass index (BMI), as well as belt upper anchorage location. The current research study examined belt positioning and fit in rear seating conditions with fixed seat back angles and a range of lower extremity postures. Lap‐belt and shoulder‐belt fit were measured in a rear seat mockup for 89 men and women with a wide range of body size and age. On average, the participants wore the lap belt fully above the anterior superior iliac spine landmark on the pelvis. High BMI was associated with occupants wearing the belt in higher and more‐forward lap‐belt positions. An increase in thigh angle relative to horizontal, which may occur with lower seat heights and constrained foot positions, was associated with occupants using higher lap belt positions. Age also had significant effects on how the lap and shoulder belt was worn, as did belt anchorage locations. These results suggest that continued research is needed to determine effective interventions to improve belt wearing and fit for rear‐seat occupants.