Newborn Weight Loss Calculator (% of Birth Weight)
Calculate your newborn's weight loss as a percentage of birth weight, see whether it is in the expected range (under 7%), needs a feeding check (7–10%) or calls for your pediatrician (10% or more), and the 7% and 10% weights.
How it works
weight loss (%) = (birth weight − current weight) ÷ birth weight × 100 · under 7% expected · 7–10% evaluate feeding · 10% or more needs medical review · 1 lb = 16 oz = 453.6 g
Almost every newborn loses some weight in the first days as extra fluid is shed and feeding gets established. Losing up to about 7% of birth weight is common, especially for breastfed babies, with the lowest point around day 3–4. A loss of 7–10% is a signal to check latch, feeding frequency and diapers with a nurse or lactation consultant, and 10% or more needs prompt medical review. Most babies are back to their birth weight by 10–14 days. Large studies (the NEWT nomograms) show weight loss also depends on hours of life and type of delivery.
Worked example
A baby born at 3,400 g who weighs 3,150 g at 48 hours has lost 250 g, which is 250 ÷ 3,400 × 100 = 7.4% of birth weight: higher than average, so it is worth having feeding checked. The 7% mark is 3,162 g and the 10% mark is 3,060 g.
Sources: Academy of Breastfeeding Medicine Protocol #3: Supplementary feedings (2017) · Flaherman VJ, et al. Early weight loss nomograms for exclusively breastfed newborns. Pediatrics 2015 · NEWT — Newborn Weight Tool
Frequently asked questions
How much weight loss is normal for a newborn?
Up to about 7% of birth weight in the first days is common, and most babies stop losing by day 3–4. Losing 10% or more is a reason to see the baby's doctor promptly.
When should a baby be back to birth weight?
Most babies regain their birth weight by 10–14 days of age. If your baby has not, the pediatrician will want to check feeding and growth.
Why do breastfed babies lose more weight?
In the first days colostrum comes in small amounts until milk "comes in" around day 2–5. Frequent feeding (8–12 times a day) helps; weight loss usually reverses once milk volume increases.
What signs mean my newborn isn't getting enough?
Fewer than about 6 wet diapers a day after day 5, dark urine or urate crystals after day 3, still passing dark meconium after day 4, poor alertness, jaundice that is getting worse, or weight loss over 10%. Call your doctor if you see these.
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Educational information only, not medical advice or a diagnosis. Discuss your results and any decision with your doctor, midwife or pharmacist.