Newborn weight loss after birth: how much is normal?

You leave the hospital with a 3.4 kg baby. Three days later, the midwife or pediatrician weighs them — they're 3.15 kg. Did something go wrong?

Almost certainly not. Newborns are expected to lose weight in the first week of life. It's so normal that hospital discharge protocols are built around it.

How much is normal

Most full-term, healthy newborns lose 5–7% of their birth weight in the first 3–5 days. By around day 10–14, they've regained it.¹

The exact pattern:

• Days 0–3: weight drops as the baby clears amniotic fluid, passes meconium, and waits for milk to come in.
• Day 3–5: weight typically reaches its lowest point (the "nadir").
• Day 5–10: weight starts climbing as feeding establishes.
• Around day 10–14: birth weight regained.

At that point, expected weight gain shifts to roughly 150–200 g (5–7 oz) per week for the first 3 months.

Why babies lose weight in the first place

Three things are happening simultaneously:

1. Fluid clearance. Babies are born with a lot of extra water — partly from amniotic fluid they swallowed, partly from IV fluids if mum had any during labour. Most of that comes out in the first 48 hours through urine and meconium.
2. Limited intake. For breastfed babies, colostrum in the first 2–3 days is calorie-dense but small in volume — a few teaspoons per feed. Mature milk doesn't fully come in until day 3–5. So intake is genuinely low for a few days.
3. Energy use. Babies are working — keeping their temperature up, breathing, learning to feed. They burn calories at the same time intake is low.

By day 5, both sides of that equation start to balance, and weight ticks back up.

What "10% rule" actually means

You'll often hear that >10% loss is the threshold. Here's what that actually triggers in practice:

• Up to 7%: considered normal. No special action.
• 7–10%: worth a feeding check. Often baby is feeding fine but a more thorough latch/intake assessment helps.
• >10%: triggers a fuller assessment — latch evaluation, possible weighed feeds, possible top-ups (expressed milk or formula), and closer monitoring until weight gain restarts.²

Birth weight regained by day 14 is the goal. If a baby still hasn't regained by then, the cause is investigated more thoroughly.

Why formula-fed babies often lose less

Babies fed formula from birth tend to lose less weight (typically 2–5%) and regain it faster. Two reasons: formula volume is consistent from feed one, and it's slightly more calorically dense than colostrum.

This is not a reason to switch — exclusive breastfeeding has well-documented benefits, and the early dip is part of the normal physiology — but it's why the loss curves look different.

When weight loss is a real problem

Call your pediatrician or midwife sooner rather than later if:

• Weight loss is more than 10% of birth weight
• Birth weight isn't regained by day 14
• Baby is having fewer than 3–4 wet nappies a day by day 4
• Baby is having fewer than 3–4 dirty nappies a day by day 4 (breastfed)
• Baby seems lethargic, hard to rouse, or uninterested in feeding
• Baby has fewer wet nappies, dry mouth, or a sunken fontanelle (dehydration)
• A breastfeeding parent has cracked nipples, severe pain, or no sense of milk coming in by day 5

These signs together suggest feeding isn't going as well as it could be — and the earlier that's caught, the easier it is to fix.

What you'll typically see at the early checks

Most countries weigh babies at:

• Birth
• Day 3–5 (often a midwife or health visitor home visit, or a pediatrician check)
• Around day 10–14 (the "back to birth weight" check)

Two to three weights in two weeks. After that, monthly weigh-ins through the first year are the norm in most systems.

Track weight from day one

Weight gain in the first month is the single most useful health signal you have. Logging each weight along with feeds and nappies gives your pediatrician a clear picture — and gives you something to look at when you're tempted to spiral about whether feeding is going well.

← Back to the complete guide: Tracking baby weight

Also in this cluster: Baby weight gain chart by age · When does baby double birth weight · Slow weight gain in breastfed babies

Sources

1. American Academy of Pediatrics. "Newborn Weight Loss." HealthyChildren.org, 2023. https://www.healthychildren.org/English/ages-stages/baby/Pages/default.aspx
2. Academy of Breastfeeding Medicine. "ABM Clinical Protocol #3: Supplementary Feedings in the Healthy Term Breastfed Neonate." Breastfeeding Medicine, 2017. https://www.bfmed.org/protocols
3. NHS. "Your baby's weight and height." NHS.uk, 2024. https://www.nhs.uk/conditions/baby/babys-development/height-weight-and-reviews/baby-height-and-weight/