Most babies gain about 1.5 to 2 pounds per month during the first three months of life, then gradually slow to about 1 to 1.25 pounds per month from months four through six. By the second half of the first year, weight gain slows further as babies become more active. These are averages, though, and the rate changes significantly as your baby grows.
The First Two Weeks: Weight Loss Is Normal
Before your baby starts gaining, they’ll actually lose weight. Most newborns drop some of their birth weight in the first few days, then begin regaining it between days three and five. About 80 percent of babies are back to their birth weight by two weeks old. A loss of up to 10 percent of birth weight is considered within the normal range, so a 7-pound baby might dip to around 6 pounds 5 ounces before turning the corner. If loss exceeds 10 percent or the baby is slow to regain, that typically prompts a closer look at feeding.
Monthly Weight Gain by Age
Weight gain is fastest in the earliest months and tapers steadily through the first year. Here’s what to expect at each stage:
- Birth to 3 months: Babies gain roughly 1 ounce per day, which works out to about 1.5 to 2 pounds per month. This is the most rapid growth phase of your baby’s life outside the womb.
- 4 to 6 months: Growth slows to an average of 1 to 1.25 pounds per month. Daily gain drops to about 20 grams (just under three-quarters of an ounce). Most babies double their birth weight somewhere around 4 to 5 months.
- 6 to 12 months: As babies start sitting, crawling, and eventually pulling to stand, they burn more calories and gain weight more slowly. Daily gain may be 10 grams or less, translating to roughly half a pound to a pound per month. By around 12 to 13 months, most boys have tripled their birth weight. Girls typically reach that milestone closer to 15 months.
So a baby born at 7.5 pounds might weigh around 15 pounds by 4 or 5 months and somewhere near 22 to 23 pounds by their first birthday. These numbers vary widely depending on genetics, feeding, and starting size.
Breastfed vs. Formula-Fed Babies
Breastfed and formula-fed babies tend to grow at a similar pace for the first three months, but after that their patterns diverge. Formula-fed infants typically gain weight more quickly after 3 months of age, while breastfed babies put on weight more slowly through the rest of the first year. This difference persists even after solid foods are introduced.
The important thing to know is that this slower gain in breastfed babies is completely normal, not a sign of inadequate nutrition. The World Health Organization growth charts, which most pediatricians now use for children under 2, are based on the growth patterns of breastfed infants specifically. If your baby is breastfed and your pediatrician is using older charts based on formula-fed populations, their growth might look like it’s lagging when it’s actually right on track. Both breastfed and formula-fed babies grow in length at similar rates; the difference is primarily in weight.
What Growth Charts Actually Tell You
Your pediatrician plots your baby’s weight on a growth chart at each visit, showing where they fall compared to other babies of the same age and sex. A baby at the 40th percentile weighs more than 40 percent of babies their age and less than the other 60 percent. There’s no “best” percentile to be on. A baby tracking steadily along the 15th percentile is growing just as healthily as one tracking along the 85th.
What matters more than any single number is the trend. Pediatricians look at whether your baby is following a consistent curve over time. A baby who has been at the 60th percentile for months and suddenly drops to the 20th is more concerning than a baby who has always been at the 10th. The rate of change tells a more useful story than any single weigh-in.
Signs That Weight Gain May Be Too Slow
Slow weight gain occasionally signals a problem called failure to thrive, which is diagnosed when a child’s weight falls below the 3rd percentile on standard growth charts or drops 20 percent below the ideal weight for their height. But a single low reading isn’t automatically a concern. Pediatricians look for a pattern: has the baby’s growth curve flattened or declined after previously following a steady trajectory?
Between checkups, some practical signs that your baby is getting enough to eat include six or more wet diapers a day after the first week, steady alertness during wake periods, and meeting developmental milestones on a roughly normal timeline. If your baby seems consistently unsatisfied after feedings, is unusually lethargic, or has fewer wet diapers than expected, it’s worth bringing up at your next visit or calling your pediatrician’s office sooner.
Why Babies Gain at Different Rates
Genetics play a large role. Tall, lean parents tend to have babies who are longer and leaner; shorter, stockier parents often have babies who carry more weight relative to their length. Premature babies follow a different trajectory entirely and are usually plotted on adjusted-age growth charts until around age 2.
Illness can cause temporary slowdowns. A baby with a bad cold who nurses less for a week might gain very little that week, then bounce back with a growth spurt once they feel better. Growth also doesn’t happen in a perfectly smooth line. Babies sometimes plateau for a week or two and then jump up, which is why pediatricians look at the big picture across several visits rather than comparing any two weigh-ins in isolation.