You don't need the base - it is just a quick way to remove the carseat from the car, or move it from car to car. The belt takes a bit more work to buckle/unbuckle each time. I've only seen bases with infant style rear-facing seats. For the convertable (rear facing to 1 year and 20 pounds, front facing after that) there is no base - the seat stays in place with the belt and you don't take it in and out of the car.