My son is 15 months and 3 days old my due date was january 23, 2013 but i had him on december 23, 2012 he weights 20lbs now. what should he weight now?

Hard to say: The appropriate weight for a given kid depends on multiple factors (height, weight , head size, pattern).This kids premature birth (1mo) places his weight at the low end of normal weights for age. It would be considered normal if he has always been growing at a slow steady rate and his length was about 29.5 inches. Growth charts are available at www.Cdc.Gov/growthcharts for review.