Baby Growth at Month 21: Milestones & Percentiles (2026)
Your baby is 21 months and each month brings visible changes. At this age, growth has shifted into toddler mode — slower and steadier, averaging 30-50g per week. The median weight is about ${11.5 kg} (${25.4 lb}) for boys and ${10.9 kg} (${24.0 lb}) for girls. The healthy range is wide — all values are reference averages for education only, not medical advice.
Avg weight (boy)
25.4 lb · 11.5 kg
Avg weight (girl)
24.0 lb · 10.9 kg
Avg length (boy)
33.5 in · 85.1 cm
Avg length (girl)
33.0 in · 83.7 cm
Avg head circ. (boy)
19.2 in · 48.8 cm
Avg head circ. (girl)
18.7 in · 47.6 cm
Weight percentiles at 21 months
| Percentile | Boys | Girls |
|---|---|---|
| 3th | 20.3 lb · 9.2 kg | 19.0 lb · 8.6 kg |
| 15th | 22.7 lb · 10.3 kg | 21.2 lb · 9.6 kg |
| 50th (median) | 25.4 lb · 11.5 kg | 24.0 lb · 10.9 kg |
| 85th | 28.4 lb · 12.9 kg | 27.1 lb · 12.3 kg |
| 97th | 32.0 lb · 14.5 kg | 30.9 lb · 14.0 kg |
Length percentiles at 21 months
| Percentile | Boys | Girls |
|---|---|---|
| 3th | 31.3 in · 79.4 cm | 30.5 in · 77.5 cm |
| 15th | 32.4 in · 82.3 cm | 31.7 in · 80.6 cm |
| 50th (median) | 33.5 in · 85.1 cm | 33.0 in · 83.7 cm |
| 85th | 34.6 in · 88.0 cm | 34.1 in · 86.7 cm |
| 97th | 35.8 in · 90.9 cm | 35.4 in · 89.8 cm |
Head circumference percentiles at 21 months
| Percentile | Boys | Girls |
|---|---|---|
| 3th | 18.2 in · 46.3 cm | 17.8 in · 45.2 cm |
| 15th | 18.7 in · 47.5 cm | 18.3 in · 46.4 cm |
| 50th (median) | 19.2 in · 48.8 cm | 18.7 in · 47.6 cm |
| 85th | 19.7 in · 50.1 cm | 19.2 in · 48.8 cm |
| 97th | 20.2 in · 51.4 cm | 19.7 in · 50.0 cm |
Growth at 21 months: what the numbers mean
Growth at 21 months is gradual. On WHO reference charts, a baby at the 50th percentile weighs about 11.5 kg (25.4 lb) for boys and 10.9 kg (24.0 lb) for girls. Median length: 85.1 cm (33.5 in) for boys, 83.7 cm (33.0 in) for girls. Median head circumference: 48.8 cm (19.2 in) for boys, 47.6 cm (18.7 in) for girls. Toddler growth is intentionally slower. A toddler might gain only 1-2 kg (2-4 lb) in the entire second year. The rapid doubling of birth weight that happened in months 0-4 slows to a gradual climb. The single most important principle: pediatricians watch the trend across multiple visits, not any single number. A baby tracking the 15th percentile steadily is thriving as much as one at the 85th. A sudden crossing of several percentile lines gets attention — and often turns out to be measurement error, a growth spurt, or a temporary feeding bump. These values are educational references, not medical advice.
Feeding at 21 months
At 21 months, your toddler eats mostly table foods. Three meals and 2-3 snacks daily is typical. Caloric needs: 1000-1300 calories. Appetite swings day to day — eating everything one day, surviving on crackers the next — are normal toddler behavior. Portions: about 1 tablespoon per year of age per food group. Whole milk (after 12 months): 16-24 oz/day — more can reduce appetite for iron-rich solids.
Sleep at 21 months
Total sleep: 11-14 hours — 10-12 at night plus 1 nap. Most toddlers on one afternoon nap. Night waking may be teething, separation anxiety, or developmental excitement (walking, talking disrupt sleep temporarily).
Play and development at 21 months
Your 21-month-old is a busy explorer. Running, climbing, jumping are main events. Complex pretend play emerges — kitchen set, dolls, toy tools. Reading daily builds vocabulary; ask questions about pictures. Outdoor time provides rich sensory input. Limit screen time — hands-on play is where learning happens.
Milestones at 21 months
Every baby develops on their own timeline. These are typical skills many babies show around this age. If your baby misses several milestones, mention it to your pediatrician.
- 1Walks down stairs with help, facing forward, holding railing or your hand.
- 2Uses two-word phrases consistently — 'daddy go,' 'my turn,' 'big truck.'
- 3Names several pictures in a book when asked 'what is that?'
- 4Shows independence at mealtime — wants own spoon, chooses between two snacks.
When to call your pediatrician
- Cannot run or walks very unsteadily
- No two-word phrases by 24 months
- Does not imitate actions/words; shows little interest in others
- Loses previously acquired language, social, or motor skills
- Crossing more than 2 major percentile lines between visits
BabyPercent is educational only and not a substitute for professional medical advice.
Frequently asked questions
What is the average weight for a 21 months baby?
At the 50th percentile on WHO charts, a 21-month-old boy weighs about 11.5 kg (25.4 lb) and a girl about 10.9 kg (24.0 lb). The healthy range from the 3rd to 97th percentile is wide. These are reference averages for education, not medical advice.
What is the average length of a 21 months baby?
At the 50th percentile, a 21-month-old boy measures about 85.1 cm (33.5 in) and a girl about 83.7 cm (33.0 in). Babies under 24 months are measured lying down (recumbent length). Reference averages only.
What is the average head size at 21 months?
At the 50th percentile, head circumference is about 48.8 cm (19.2 in) for boys and 47.6 cm (18.7 in) for girls. Head circumference is measured at every well-baby visit because it reflects healthy brain growth. Educational reference only.
When should I worry about my 21-month-old's growth?
A single number rarely matters. Call your pediatrician if your baby crosses several percentile lines between visits, is not feeding well, has very few wet diapers, or seems unusually lethargic. Trust your gut — when in doubt, call. BabyPercent is educational only, not medical advice.
WHO vs CDC growth charts — which one should I use?
The WHO charts (used by most pediatricians worldwide) are based on healthy, breastfed babies from six countries. CDC charts are based on a US reference population. For babies 0-24 months, WHO charts are the standard recommended by the CDC and AAP. Both are available on BabyPercent for comparison.
Is my 21-month-old growing enough?
Growth has slowed compared to the newborn phase — this is normal. Toddler growth is slow and steady. Your 21-month-old might gain only 1-2 kg (2-4 lb) in the entire second year. As long as they follow their curve, they are growing well.
How many naps should my 21-month-old take?
Most 21-month-olds take 1 nap lasting 1.5-2.5 hours in the early afternoon. Night sleep is typically 10-12 hours. Some toddlers drop the nap around age 3, but most still need it.