What do growth percentiles mean?

A percentile shows how your baby compares to other babies of the same age and sex. The 50th percentile is the median. A baby at the 25th percentile weighs more than 25% and less than 75% of babies the same age — all percentiles within the 3rd to 97th range are considered normal.

Should I be concerned if my baby is below the 50th percentile?

No. Any percentile from the 3rd to 97th is within the normal range. What matters most is consistent growth along the same percentile curve over time. A drop across two or more major percentile lines warrants discussion with your pediatrician.

How often should I track my baby's growth?

Pediatricians typically measure growth at well-child visits: 2, 4, 6, 9, 12, 15, 18, 24, and 30 months. Home measurements between visits can help monitor trends.

What is preterm corrected age?

Babies born before 37 weeks should have their age corrected until 24 months: corrected age = actual age minus weeks premature. For example, a 6-month-old born 4 weeks early has a corrected age of about 5 months for growth assessment.

Baby Growth Calculator

Calculate your baby's weight and length percentiles by age using WHO/CDC growth chart approximations. Track growth trends and check developmental milestones.

Baby Age

months

Weight ?

lbs

Length ?

Sex

Weight Percentile

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Length Percentile —

Interpretation —

Average Weight at This Age —

Extended More scenarios, charts & detailed breakdown ▾

Age

months

Weight

lbs

Length

Head Circumference ?

Sex

Weight Percentile

—

Length Percentile —

Head Circumference Percentile —

Weight-for-Length Assessment —

Overall Interpretation —

Professional Full parameters & maximum detail ▾

Sex

Age

months

Weight

lbs

Length

Head Circumference

Gestational Age at Birth ?

weeks

Percentiles

Weight Percentile —

Length Percentile —

Head Circumference Percentile —

Z-Scores & Composition

Weight-for-Length —

BMI-for-Age (2+ yrs) —

Weight Z-Score —

Length Z-Score —

Clinical Notes

Corrected Age (if preterm) —

Growth Assessment —

How to Use This Calculator

Enter your baby's age in months, current weight in pounds, length in inches, and sex.
The calculator estimates weight and length percentiles using WHO/CDC growth chart approximations.
Use the Growth Tracking tab to enter 3 measurements at different ages and see the trend.
Use the Milestone Check tab to see expected developmental milestones for any age.

Formula

Percentile estimated from z-score: z = (measured value − age/sex mean) / SD
WHO mean weight (boys, 6 months) ≈ 7.9 kg | WHO mean length (boys, 6 months) ≈ 67.6 cm
Results are approximations — use official WHO/CDC charts for clinical decisions.

Example

Example: A 6-month-old boy weighing 16 lbs (7.3 kg), length 26 in (66 cm): z-weight ≈ −0.6 (≈ 25th–50th percentile), z-length ≈ −0.6 (≈ 25th–50th percentile) — normal growth.

Frequently Asked Questions

A percentile shows how your baby compares to other babies of the same age and sex. The 50th percentile is the median. A baby at the 25th percentile weighs more than 25% and less than 75% of babies the same age — all percentiles within the 3rd to 97th range are considered normal.
No. Any percentile from the 3rd to 97th is within the normal range. What matters most is consistent growth along the same percentile curve over time. A drop across two or more major percentile lines warrants discussion with your pediatrician.
Pediatricians typically measure growth at well-child visits: 2, 4, 6, 9, 12, 15, 18, 24, and 30 months. Home measurements between visits can help monitor trends.
Babies born before 37 weeks should have their age corrected until 24 months: corrected age = actual age minus weeks premature. For example, a 6-month-old born 4 weeks early has a corrected age of about 5 months for growth assessment.

Related Calculators

Sources & References (5) ▾