The weight math of week two

Medically-informed · Sources: MedlinePlus · Updated June 2026 · 3 min read

Down before up

Newborns commonly lose up to about 7–10% of birth weight in the first days — mostly fluid — and regain it by around two weeks. The dip terrifies parents and rarely surprises pediatricians.

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Why the dip happens

Babies are born pre-loaded with extra fluid for the transition while milk supply ramps up. The scale reads that handoff, not a feeding failure.

Is this normal for your baby?

FirstWeeks answers with your baby’s age and today’s log in mind — with pediatric sources attached.

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What actually matters

The trend and the diapers. Regular feeds, six-plus wets a day and steady stools say intake is working better than any single weigh-in — home scales mislead more than they help.

The two-week visit

That checkup exists largely for this: confirming baby is back to birth weight or clearly heading there. If not, the pediatrician adjusts the feeding plan with you — it's a fixable logistics problem, not a verdict.

Worth a call sooner

Fewer wet diapers, a sleepy baby who's hard to wake for feeds, or feeding refusal — don't wait for the scheduled visit.