The most common method is using a thermometer. Insert the thermometer in the thickest part of the chicken, usually the thigh, and away from any bones. The chicken should be done cooking when its internal temperature reaches 165F - 170F. Or you can determine roasted chicken doneness by looking at the color of its juice. If the juice from the cavity is clear that indicates roasted chicken is done. If the juice is cloudy or pink, the chicken is undercooked.