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Baby Weight Growth Velocity Calculator

Enter two weight measurements with dates to calculate your baby's weight gain in g/day and oz/week — and compare to WHO expected growth rates for their age and sex.

Measurement #1

Measurement #2

Enter two weight measurements at least 1 week apart. Results compare to WHO growth velocity standards.

WHO Weight Velocity Reference (g/day)

AgeBoys (g/day)Girls (g/day)Approx weekly oz
0–2 months24–3521–305.6–8.0 oz
2–4 months17–2514–223.8–5.8 oz
4–6 months12–2010–182.7–4.7 oz
6–9 months9–157–142.0–3.6 oz
9–12 months7–136–121.6–3.1 oz
12–18 months5–104–91.1–2.3 oz
18–24 months4–84–81.0–2.0 oz
24+ months3–73–70.7–1.7 oz

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Weight Velocity: A Better Window Into Baby's Growth

A single weight measurement tells you where your baby is today. Weight velocity tells you the direction and speed of travel. Two babies can both be at the 25th percentile for weight — but one is trending upward and one trending downward. They have very different growth stories. Weight velocity, measured in grams per day, is the cleaner signal that helps pediatricians spot faltering growth early and reassure parents whose babies are growing healthily but slowly.

The WHO Weight Velocity Reference: What It Measures

The WHO Child Growth Standards include velocity tables (published 2009) derived from the MGRS longitudinal study — the same study that produced the single-measurement growth charts. The standards give weight velocity by age, sex, and measurement interval. This tool uses the daily gain ranges for each age group to classify whether a baby's growth rate falls within, below, or above the expected range.

Breastfed vs. Formula-Fed Weight Gain Patterns

🤱 Breastfed Babies

  • • Typically gain weight slightly faster in months 1–3
  • • Naturally gain more slowly from 4–12 months vs. formula
  • • WHO charts were designed for breastfed babies as the reference
  • • Lower weight on WHO charts may not indicate a problem

🍼 Formula-Fed Babies

  • • Often gain faster in months 3–12 than WHO reference
  • • CDC charts (breastfed + formula-fed) tend to plot higher
  • • Higher velocity on this tool may be normal for formula-fed babies
  • • Discuss with pediatrician if velocity is consistently very high

Signs of Adequate Feeding Beyond the Scale

👶6+ wet diapers per day after day 5 (breastfed)
💤Sleepy but rousable — not persistently lethargic
📈Weight tracking upward at a consistent rate
😊Alert and engaged when awake between feeds
🤱Satisfied (not crying) for at least 1–2 hours after feeds
🌱Length and head circumference growing normally

Frequently Asked Questions

How much weight should a baby gain per week?

Weight gain varies significantly by age. In the first 2 months, babies typically gain 24–35 g/day (about 5–8.5 oz/week) for boys and 21–30 g/day (about 5–7.5 oz/week) for girls. By 6 months, the rate slows to 9–15 g/day. By 12 months, babies gain 7–13 g/day. These ranges are based on WHO Child Growth Standards velocity tables and represent the middle 80% of healthy babies.

Is it normal for weight gain to slow down after 3 months?

Yes — this is completely normal and expected. The rapid gain of the newborn period (sometimes 200g+ per week) naturally decelerates as babies grow. The slowing is built into WHO velocity standards. A baby who gained 30g/day in month 1 and gains 15g/day in month 4 is growing perfectly normally — the rate change is expected.

My baby gained weight more slowly than expected. Should I be worried?

One measurement interval showing slightly-below-average velocity is rarely cause for immediate concern. Velocity can be affected by illness, teething, feed refusal during a developmental leap, or simply a few days of reduced intake. What matters is the trend: consistently low velocity over multiple measurement periods, combined with crossing percentile lines downward on the growth chart, is more significant.

What is considered poor weight gain (faltering growth)?

Clinically significant 'faltering growth' (previously called 'failure to thrive') is typically defined as weight falling more than 2 standard deviations below the expected growth curve, or weight-for-age crossing two major percentile lines downward. For velocity, concern is raised when gain is persistently below 10–15g/day in a young infant or below 5–7 g/day in an older baby.

How often should I weigh my baby?

Most pediatricians weigh babies at every well-child visit (which at its most frequent is every 1–2 months in the first year). Weighing more frequently than every 1–2 weeks for a healthy baby isn't typically recommended — it can cause unnecessary anxiety and home scales are less accurate than clinical scales. If there's a specific concern, your pediatrician may recommend more frequent weight checks.

Why might my baby gain weight faster than expected?

Rapid weight gain can sometimes occur during catch-up growth (after an illness), after a period of poor intake, or simply during a growth spurt. Formula-fed babies may gain slightly faster than breastfed babies in the first few months. Consistently very high velocity above the 97th percentile is worth mentioning to your pediatrician, as it may be associated with later obesity risk — though it's often benign.

Can I weigh my baby at home?

Home baby scales can provide a general indication, but clinical scales are more accurate. Home measurements vary by up to 100–200g depending on scale quality and weighing conditions (clothing, timing relative to feeds). For velocity calculations, consistent measurement conditions (same scale, same time of day, before feeds, without clothes) reduce error. Differences of less than 100–200g over 2 weeks should not be over-interpreted.

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