Physical Development

Baby Not Growing Fast Enough - Failure to Thrive

Medically reviewed by Dr. Sarah Chen, MD, FAAP · Board-Certified Pediatrician

Content reviewed against published AAP, WHO, AAP guidelines

Editorial policy

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Your baby's physical development is unique, and concerns about baby not growing fast enough - failure to thrive, here is what you need to know.

The short answer

Slow weight gain (falling across percentile lines on the growth chart) can have many causes, ranging from simple (not getting enough calories, growth pattern recalibration) to medical (feeding difficulties, food allergies, malabsorption, or underlying conditions). "Failure to thrive" is a clinical term for weight that falls below the 2nd percentile or drops across two major percentile lines. The most common cause is insufficient caloric intake - the baby is not eating enough, not absorbing enough, or burning too many calories. Early evaluation is important because nutrition affects brain development.

Key takeaways

  • Slow weight gain (falling across percentile lines on the growth chart) can have many causes, ranging from simple (not getting enough calories, growth pattern recalibration) to medical (feeding difficulties, food allergies, malabsorption, or underlying conditions). "Failure to thrive" is a clinical term for weight that falls below the 2nd percentile or drops across two major percentile lines. The most common cause is insufficient caloric intake - the baby is not eating enough, not absorbing enough, or burning too many calories. Early evaluation is important because nutrition affects brain development.
  • Usually normal when: Your baby dropped from a high birth percentile to a lower one by 6 months and then tracked steadily - this is genetic recalibration
  • Call your doctor if: Your baby has dropped across two or more percentile lines or fallen below the 2nd percentile
  • Varies by age — see the age-by-age breakdown below
“Supervised tummy time is recommended daily from the time the baby comes home from the hospital to help prevent flat head syndrome and to strengthen neck and shoulder muscles.”
— Back to Sleep, Tummy to Play, American Academy of Pediatrics (AAP)

This is one of the most common questions parents ask. Searching for answers means you care.

What Parents Should Know

According to AAP, WHO guidelines, slow weight gain (falling across percentile lines on the growth chart) can have many causes, ranging from simple (not getting enough calories, growth pattern recalibration) to medical (feeding difficulties, food allergies, malabsorption, or underlying conditions). "Failure to thrive" is a clinical term for weight that falls below the 2nd percentile or drops across two major percentile lines. The most common cause is insufficient caloric intake - the baby is not eating enough, not absorbing enough, or burning too many calories. Early evaluation is important because nutrition affects brain development. At 0-3 months, newborns lose up to 7-10% of birth weight in the first week and should regain it by 2 weeks. After that, expect about 1 oz per day (6-7 oz per week) of weight gain. If your newborn has not regained birth weight by 2 weeks, feeding should be evaluated. Breastfed babies with slow gain may need: more frequent feeds, better latch assessment, supplementation while increasing supply, or evaluation for tongue tie. Formula-fed babies with slow gain may need: more frequent feeds, concentrated formula, or evaluation for feeding difficulties. It is generally considered normal when your baby dropped from a high birth percentile to a lower one by 6 months and then tracked steadily - this is genetic recalibration. However, you should contact your pediatrician promptly if your baby has dropped across two or more percentile lines or fallen below the 2nd percentile.

Sources: [1], [2], [3]

Normal vs. Concerning

Usually Normal
Worth Discussing
Your baby dropped from a high birth percentile to a lower one by 6 months and then tracked steadily - this is genetic recalibration
Your baby has dropped across two or more percentile lines or fallen below the 2nd percentile
Your baby is small (low percentile) but has always tracked along the same curve and is meeting milestones
Your newborn has not regained birth weight by 3 weeks
Your breastfed baby is gaining slower than formula-fed peers but is still following their curve
Your baby is lethargic, not feeding, and appears dehydrated alongside poor growth
Your toddler's weight plateaued briefly during an active developmental period like learning to walk
Your baby is losing weight (not just gaining slowly)

By Age

What to expect by age

0-3 months

Newborns lose up to 7-10% of birth weight in the first week and should regain it by 2 weeks. After that, expect about 1 oz per day (6-7 oz per week) of weight gain. If your newborn has not regained birth weight by 2 weeks, feeding should be evaluated. Breastfed babies with slow gain may need: more frequent feeds, better latch assessment, supplementation while increasing supply, or evaluation for tongue tie. Formula-fed babies with slow gain may need: more frequent feeds, concentrated formula, or evaluation for feeding difficulties.

3-6 months

Weight gain typically slows to about 4-5 oz per week. A drop of one percentile line can be normal (genetic recalibration - large newborns of small parents may settle into lower percentile). But dropping across two percentile lines is a concern. If your baby is feeding well but not gaining, your pediatrician may check for: cow's milk protein allergy (especially if there is blood in stool or eczema), reflux causing food refusal, or malabsorption. Frequent weight checks (every 1-2 weeks) help track the pattern.

6-12 months

Weight gain continues to slow naturally to about 3-4 oz per week. Active babies who are crawling and pulling up may have periods of slower gain because they are burning more calories. If your baby is small but following their own curve, eating solids with interest, and meeting milestones, they are likely fine. If weight continues to drop off their curve, your pediatrician may suggest: calorie-dense foods (avocado, nut butters, olive oil), fortified formula, or evaluation for underlying conditions.

12-36 months

Toddlers are notoriously picky and may eat very little some days. Weight gain slows to about 3-5 pounds per year. If your toddler is active, meeting milestones, and following their own growth curve (even if it is a low percentile), they are likely growing appropriately. Concern arises if: weight drops off their established curve, they are crossing percentile lines downward, they have very limited dietary intake, or they seem lethargic and unwell alongside poor growth.

What to Tell Your Pediatrician

  • Describe when you first noticed baby not growing fast enough - failure to thrive and how it has changed over time.
  • Note your baby's current age and which age-specific patterns you are seeing.
  • Mention if your baby has dropped across one major percentile line on the growth chart.
  • Mention if your baby is gaining less than expected despite adequate feeding.
  • Let your doctor know if you have noticed any related concerns, such as changes in feeding, sleep, or movement patterns.
  • Bring a list of any questions or observations you want to discuss at the appointment.

What Should You Do?

When to take action

Probably normal when...
  • Your baby dropped from a high birth percentile to a lower one by 6 months and then tracked steadily - this is genetic recalibration
  • Your baby is small (low percentile) but has always tracked along the same curve and is meeting milestones
  • Your breastfed baby is gaining slower than formula-fed peers but is still following their curve
  • Your toddler's weight plateaued briefly during an active developmental period like learning to walk
Mention at your next visit when...
  • Your baby has dropped across one major percentile line on the growth chart
  • Your baby is gaining less than expected despite adequate feeding
  • Your baby is small and also seems excessively tired or not meeting developmental milestones
  • You are struggling to get your baby to eat enough and need feeding support
Act now when...
  • Your baby has dropped across two or more percentile lines or fallen below the 2nd percentile
  • Your newborn has not regained birth weight by 3 weeks
  • Your baby is lethargic, not feeding, and appears dehydrated alongside poor growth
  • Your baby is losing weight (not just gaining slowly)

What You Can Do at Home

  • Keep track of when you notice baby not growing fast enough - failure to thrive — noting the time of day, duration, and any triggers can help your pediatrician.
  • Remember that your baby dropped from a high birth percentile to a lower one by 6 months and then tracked steadily - this is genetic recalibration — this is generally within the range of normal.
  • At 0-3 months, focus on observation rather than intervention unless your pediatrician advises otherwise.
  • Provide plenty of supervised floor time and tummy time to support your baby's physical development.
  • While monitoring at home, seek immediate care if your baby has dropped across two or more percentile lines or fallen below the 2nd percentile.

Baby Growing Too Fast - Rapid Weight or Height Gain

Babies come in all sizes, and being on a high growth percentile does not automatically mean something is wrong. What matters more than the percentile itself is the pattern - a baby who has always tracked along the 90th percentile is following their own normal curve. Rapid upward crossing of percentile lines (jumping from the 50th to the 95th) is more noteworthy. Breastfed babies cannot be overfed at the breast. For formula-fed babies, ensure appropriate bottle feeding practices. Most "big babies" simply have big parents and are growing as genetically programmed.

Baby Not Growing Taller - Short Stature Concerns

Height (length) is primarily determined by genetics - if parents are shorter, their child will likely be shorter. A baby who is consistently at a low height percentile but follows their own curve is most likely genetically small. Concern arises when a child's length drops across percentile lines or when length is significantly lower than what would be expected based on parental heights. Growth hormone deficiency, thyroid issues, and certain genetic conditions can affect height, but these are uncommon. Most short children are simply constitutionally short or have constitutional growth delay (late bloomers).

Signs of Nutritional Deficiency in Toddlers

The most common nutritional deficiencies in toddlers are iron, vitamin D, zinc, and calcium - especially in picky eaters and children who drink excessive amounts of milk. Signs of iron deficiency (the most common) include pallor, fatigue, irritability, poor appetite, and slow weight gain. Most picky toddlers get adequate nutrition despite their limited diets, but if your child eats fewer than 10-15 foods total or avoids entire food groups, a nutritional evaluation may be helpful.

Tool

Growth Percentile Calculator

Plot your baby's weight, length, and head circumference on WHO/CDC growth charts.

Milestone

Month-by-Month Development

Detailed monthly development guides from birth through 24 months.

Guide

When to Call the Doctor

General guide on when to call the pediatrician, visit urgent care, or go to the ER.

Frequently asked questions

Is baby not growing fast enough - failure to thrive normal?
Slow weight gain (falling across percentile lines on the growth chart) can have many causes, ranging from simple (not getting enough calories, growth pattern recalibration) to medical (feeding difficulties, food allergies, malabsorption, or underlying conditions). "Failure to thrive" is a clinical term for weight that falls below the 2nd percentile or drops across two major percentile lines. The most common cause is insufficient caloric intake - the baby is not eating enough, not absorbing enough, or burning too many calories. Early evaluation is important because nutrition affects brain development.
When should I call the doctor about baby not growing fast enough - failure to thrive?
Your baby has dropped across two or more percentile lines or fallen below the 2nd percentile Your newborn has not regained birth weight by 3 weeks Your baby is lethargic, not feeding, and appears dehydrated alongside poor growth
When is baby not growing fast enough - failure to thrive normal?
Your baby dropped from a high birth percentile to a lower one by 6 months and then tracked steadily - this is genetic recalibration Your baby is small (low percentile) but has always tracked along the same curve and is meeting milestones Your breastfed baby is gaining slower than formula-fed peers but is still following their curve
What causes baby not growing fast enough - failure to thrive?
Slow weight gain (falling across percentile lines on the growth chart) can have many causes, ranging from simple (not getting enough calories, growth pattern recalibration) to medical (feeding difficulties, food allergies, malabsorption, or underlying conditions). "Failure to thrive" is a clinical term for weight that falls below the 2nd percentile or drops across two major percentile lines. The most common cause is insufficient caloric intake - the baby is not eating enough, not absorbing enough, or burning too many calories. Early evaluation is important because nutrition affects brain development. Common explanations include: Your baby dropped from a high birth percentile to a lower one by 6 months and then tracked steadily - this is genetic recalibration. Your baby is small (low percentile) but has always tracked along the same curve and is meeting milestones.
What should I mention to my pediatrician about baby not growing fast enough - failure to thrive?
You should mention baby not growing fast enough - failure to thrive at your next visit if: Your baby has dropped across one major percentile line on the growth chart. Your baby is gaining less than expected despite adequate feeding. Your baby is small and also seems excessively tired or not meeting developmental milestones.
Is baby not growing fast enough - failure to thrive normal at 0-3 months?
Newborns lose up to 7-10% of birth weight in the first week and should regain it by 2 weeks. After that, expect about 1 oz per day (6-7 oz per week) of weight gain. If your newborn has not regained birth weight by 2 weeks, feeding should be evaluated. Breastfed babies with slow gain may need: more frequent feeds, better latch assessment, supplementation while increasing supply, or evaluation for tongue tie. Formula-fed babies with slow gain may need: more frequent feeds, concentrated formula, or evaluation for feeding difficulties.
Is baby not growing fast enough - failure to thrive normal at 3-6 months?
Weight gain typically slows to about 4-5 oz per week. A drop of one percentile line can be normal (genetic recalibration - large newborns of small parents may settle into lower percentile). But dropping across two percentile lines is a concern. If your baby is feeding well but not gaining, your pediatrician may check for: cow's milk protein allergy (especially if there is blood in stool or eczema), reflux causing food refusal, or malabsorption. Frequent weight checks (every 1-2 weeks) help track the pattern.
Should I go to the ER for baby not growing fast enough - failure to thrive?
Seek emergency care if your baby has dropped across two or more percentile lines or fallen below the 2nd percentile, or if your newborn has not regained birth weight by 3 weeks. When in doubt, call your pediatrician's after-hours line for guidance.
Does baby not growing fast enough - failure to thrive go away on its own?
In many cases, baby not growing fast enough - failure to thrive resolves on its own, especially when your baby dropped from a high birth percentile to a lower one by 6 months and then tracked steadily - this is genetic recalibration. By 12-36 months, toddlers are notoriously picky and may eat very little some days. Weight gain slows to about 3-5 pounds per year. If your toddler is active, meeting milestones, and following their own growth curve (even if it is a low percentile), they are likely growing appropriately. Concern arises if: weight drops off their established curve, they are crossing percentile lines downward, they have very limited dietary intake, or they seem lethargic and unwell alongside poor growth.
AAPWHOAAP

References

  1. [1]Jaffe AC. Failure to Thrive: Current Clinical Concepts. Pediatrics in Review. 2011. AAP
  2. [2]World Health Organization. Child Growth Standards. WHO
  3. [3]American Academy of Pediatrics. Is Your Baby Growing Normally? HealthyChildren.org. AAP

Doctor Visit Checklist

Bring this checklist to your next pediatrician visit to discuss Baby Not Growing Fast Enough - Failure to Thrive.

Things to mention

  • Describe when you first noticed baby not growing fast enough - failure to thrive and how it has changed over time.
  • Note your baby's current age and which age-specific patterns you are seeing.
  • Mention if your baby has dropped across one major percentile line on the growth chart.
  • Mention if your baby is gaining less than expected despite adequate feeding.
  • Let your doctor know if you have noticed any related concerns, such as changes in feeding, sleep, or movement patterns.
  • Bring a list of any questions or observations you want to discuss at the appointment.

Observations to share

  • Your baby has dropped across one major percentile line on the growth chart
  • Your baby is gaining less than expected despite adequate feeding
  • Your baby is small and also seems excessively tired or not meeting developmental milestones

Urgent signs to report immediately

  • Your baby has dropped across two or more percentile lines or fallen below the 2nd percentile
  • Your newborn has not regained birth weight by 3 weeks
  • Your baby is lethargic, not feeding, and appears dehydrated alongside poor growth

My notes

From ismybabyalright.com — free, evidence-based baby health guides

All content follows our editorial policy and is reviewed against published clinical guidelines.

2,705 evidence-based guides6 authoritative medical sources5 medical advisory board members

Related Resources

Growth Spurts TimelineGrowth Percentile CalculatorDevelopmental ActivitiesEmergency ContactsBaby Tracker

Bottom line

Most cases of baby not growing fast enough - failure to thrive are normal. Talk to your pediatrician if your baby has dropped across two or more percentile lines or fallen below the 2nd percentile.

Trust your instincts. If something feels wrong, reach out to your pediatrician. Worrying about your baby means you care — that is a good thing.

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Related Physical Concerns

Baby Growing Too Fast - Rapid Weight or Height Gain

Babies come in all sizes, and being on a high growth percentile does not automatically mean something is wrong. What matters more than the percentile itself is the pattern - a baby who has always tracked along the 90th percentile is following their own normal curve. Rapid upward crossing of percentile lines (jumping from the 50th to the 95th) is more noteworthy. Breastfed babies cannot be overfed at the breast. For formula-fed babies, ensure appropriate bottle feeding practices. Most "big babies" simply have big parents and are growing as genetically programmed.

Baby Not Growing Taller - Short Stature Concerns

Height (length) is primarily determined by genetics - if parents are shorter, their child will likely be shorter. A baby who is consistently at a low height percentile but follows their own curve is most likely genetically small. Concern arises when a child's length drops across percentile lines or when length is significantly lower than what would be expected based on parental heights. Growth hormone deficiency, thyroid issues, and certain genetic conditions can affect height, but these are uncommon. Most short children are simply constitutionally short or have constitutional growth delay (late bloomers).

Signs of Nutritional Deficiency in Toddlers

The most common nutritional deficiencies in toddlers are iron, vitamin D, zinc, and calcium - especially in picky eaters and children who drink excessive amounts of milk. Signs of iron deficiency (the most common) include pallor, fatigue, irritability, poor appetite, and slow weight gain. Most picky toddlers get adequate nutrition despite their limited diets, but if your child eats fewer than 10-15 foods total or avoids entire food groups, a nutritional evaluation may be helpful.

Should I Use Adjusted Age for My Preemie's Milestones?

Yes — for premature babies, developmental milestones should be assessed using adjusted (corrected) age, not chronological age, until at least 2 years of age. Adjusted age is calculated by subtracting the number of weeks your baby was born early from their actual age. For example, a 6-month-old born 2 months early would have an adjusted age of 4 months, and should be assessed against 4-month milestones. Most pediatricians use adjusted age for developmental assessment through age 2-3, and for growth charts through age 2.

Baby-Proofing a Small Apartment

Baby-proofing a small apartment is absolutely possible and focuses on the same key safety principles as any home: securing furniture to walls, covering outlets, locking cabinets with hazardous materials, and ensuring safe sleep spaces. Small spaces actually have an advantage - there is less area to monitor. Focus on eliminating the most dangerous hazards first: falls, poisoning, choking, and burns.

My Baby Seems to Use One Side More Than the Other

Babies should use both sides of their body fairly equally during the first 18 months of life. While slight preferences can be normal, a consistent pattern of favoring one side - using one arm much more than the other, crawling with one leg dragging, or turning the head predominantly one way - should always be discussed with your pediatrician. Early identification of asymmetry leads to the best outcomes.