How to Figure Out What Percentage of Birth Weight Is Lost

Newborns normally lose weight in the first week of their lives. Breastfed babies usually lose seven to 10 percent of their birth weights, while babies who are fed formula typically lose around five percent. Hospitals weigh newborns frequently and monitor changes in their weight carefully 1. If you have concerns about the percentage of birth weight that your baby has lost, you may find it reassuring to monitor your baby's weight at home.

Weigh your baby. Many scales weigh using pounds and ounces (an ounce equals one-sixteenth of a pound). To avoid complicated calculations using fractions, use your scale's metric setting, or convert the pounds-and-ounces figure to a decimal by dividing the number of ounces by sixteen. For example, if your child weighs 6 lb., 10 oz., divide 10 by 16 to determine that your child weighs 6.63 lb.

Subtract your baby's current weight from her birth weight 1. This will allow you to determine how much weight she has lost.

Divide the amount of weight your baby has lost by his birth weight. Remember to use grams -- the metric measurement -- or to convert your baby's birth weight into a decimal by dividing the number of ounces by sixteen.

Multiply the result by 100 to convert your answer to a percentage.


Always use the same units of measurement when calculating. If you are measuring your child's weight using grams, use your baby's birth weight in grams for your calculation.

Weigh your baby at a time neither immediately before nor after feeding. Feeding causes small changes in a baby's weight that impact the calculation of percentage of birth weight lost.


Contact your doctor if you have any concerns about the weight or development of your newborn.

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