hi ray, i find the website is giving good guidelines, relative to your goals; it cannot give you a 100% accurate measurement, as each organism is different, and each food is different, but it can compare your data inputs, to your results. if your result is to loose weight, or to achieve a certain body measurement, it can track your efforts, and guide you.
if terms of carbs, if you input each and every food you eat, every day, it will give you an estimate of your carbs consumption in the day.
i don't think it's all in the carbs, though, in the end of the day it all comes down to balanced nutrition, and not burning less calories than you eat...
i hope that answers it.