Abstract: A belt shortening device intended for use with a vehicle seat belt securing a baby seat in a vehicle is constructed and arranged so that it is easily mounted to the existing seat belt without detaching the belt from its existing connection. The device includes a flat, rectangular housing having spaced slots extending across the top wall, and further includes first and second take up arms slidably mounted within the housing. The take up arms each consist of a body portion having inner and outer ends, and an elongated rack member having a first end pivotably mounted to the inner end of the body portion. The outer ends of the body portions of the take up arms include a transverse slot for receiving the seat belt therein. The take up arms are movable within the housing between an extended position wherein the outer ends of the take up arms extend outside of the housing through the slots, and a withdrawn position wherein the outer ends of the take up arms are withdrawn inside the housing.