Key points
- Weight gain: about 30 g/day at 0–3 months, 20 g/day at 3–6 months and 10 g/day for the rest of the first year.
- Term birth weight doubles by about 4 months, triples by 12 months and quadruples by 24 months.
- Length grows about 50% in the first year, doubles by 4 years and triples by 13 years.
- From 2 years to puberty: about 2 kg (4–5 lb) and, from 4 years, about 2 inches (5 cm) a year.
- US charts: WHO growth standards from birth to 2 years; CDC growth charts from 2 years onward.
- Corrected age = chronological age minus weeks born early; use it until 24 months.
Weight gain in infancy
- Term birth weight doubles by about 4 months.
- It triples by 12 months.
- It quadruples by 24 months.
| Age | Average weight gain |
|---|---|
| 0–3 months | About 30 g/day |
| 3–6 months | About 20 g/day |
| 6–12 months | About 10 g/day |
Length, height and weight after infancy
| Measure | Rule of thumb |
|---|---|
| Length in year 1 | Increases by about 50% |
| Length doubles | By about 4 years |
| Length triples | By about 13 years |
| Height gain, 4 years to adolescence | About 2 inches (5 cm) a year |
| Weight gain, 2 years to puberty | About 2 kg (4–5 lb) a year |
| Weight estimate, 1–6 years | Pounds ≈ (age in years × 5) + 17 |
| Weight estimate, 7–12 years | Pounds ≈ (age in years × 7) + 5 |
Brain growth
The brain grows fastest in the first 2 years, which is why head circumference is measured at every visit in this period.
| Age | Brain size as a share of adult size |
|---|---|
| Birth | About 25% |
| 1 year | About 75% |
| 3 years | About 80% |
| 7 years | About 90% |
Choosing the right growth chart
The WHO standards describe how healthy breastfed infants grow, so they suit the first 2 years. CDC charts are used from 2 years, when children are measured standing.
| Child | Chart | How to measure |
|---|---|---|
| Preterm infant, before term | Preterm chart, such as Fenton | Weight, length, head circumference |
| Birth to 2 years | WHO growth standards | Recumbent length, lying down |
| 2 to 20 years | CDC growth charts | Standing height |
| Down syndrome | Syndrome-specific growth chart | A child below the 3rd percentile on standard charts may be normal on these |
Corrected age for preterm infants
Corrected (adjusted) age is chronological age minus the weeks the baby was born early (40 weeks minus gestational age at birth). Plot growth and judge milestones by corrected age until 24 months.
- Example: a 12-month-old born at 29 weeks was 11 weeks (about 2½ months) early, so his corrected age is about 9½ months.
- A healthy former preterm infant who plots low on chronological-age charts: first replot by corrected age.
Common questions
How much weight should a baby gain per day?
About 30 g/day in the first 3 months, about 20 g/day from 3 to 6 months, and about 10 g/day for the rest of the first year.
Should I use WHO or CDC growth charts?
In the United States, use WHO growth standards from birth to 2 years and CDC growth charts from 2 years onward.
How long do you use corrected age for preemies?
Until 24 months. Subtract the weeks born early from chronological age when plotting growth and checking milestones.
Study this topic
Sources
- CDC 2010: Use of WHO and CDC growth charts for children aged 0–59 months (MMWR)
- CDC: Growth charts
- Fenton 2013: Revised growth chart for preterm infants (BMC Pediatrics)
- AAP 2022: Health supervision for children and adolescents with Down syndrome (Pediatrics)
Written for Pedemy in our own words from the sources above; checked November 2026. For education only, not medical advice; check doses and local protocols before treating a patient. Pedemy is independent and not affiliated with or endorsed by the organizations cited.