An infant is a child from birth through 12 months of age. That first birthday is the universal cutoff: once a child turns one year old, they are typically classified as a toddler. But the exact boundaries shift slightly depending on the context, whether you’re talking about medicine, product safety, or nutrition guidelines.
The Standard Medical Definition
In medical and public health settings, “infant” covers the entire first year of life. The CDC defines an infant death, for example, as the death of a live-born child before their first birthday. The World Health Organization uses the same 0-to-12-month window.
Within that first year, there’s an important subcategory. A newborn, or neonate, is a baby in the first 28 days of life (the first four weeks). After day 28, the child is still an infant but no longer a neonate. This distinction matters in hospitals because the neonatal period carries unique health risks and requires specialized monitoring. If you see the word “neonate” on paperwork or hear it from a pediatrician, it simply means your baby is less than four weeks old.
Why the FDA Uses a Different Range
The Food and Drug Administration extends the infant category further than most people expect. For drug safety studies and medication labeling, the FDA defines an infant as a child from one month up to two years of age. Newborns under one month get their own separate category (neonates), and children two and older fall into the “children” bracket.
This matters when you’re reading the label on an over-the-counter medication. A product labeled for “infants” in the pharmaceutical sense may be intended for children up to age two, not just babies under one. Always check the specific age and weight ranges printed on the packaging rather than relying on the word “infant” alone.
Product Safety Age Groups
The U.S. Consumer Product Safety Commission breaks the first year into three developmental windows when evaluating toys and baby gear: birth through 3 months, 4 through 7 months, and 8 through 11 months. These groupings reflect how quickly a baby’s abilities change. A toy that’s safe for a two-month-old who can only lie on their back poses different risks for a nine-month-old who can sit up, grab objects, and put everything in their mouth.
Small parts regulations apply to all toys intended for children under three years of age, which means choking hazard rules extend well beyond infancy. If you’re buying a gift for a baby, the age label on the box is based on developmental capabilities, not just a rough guess. Those labels are tied to detailed guidelines about what children at each stage can physically do.
Feeding Milestones During Infancy
For the first six months of life, breast milk or formula is a baby’s sole source of nutrition. Around six months, solid foods are gradually introduced, but milk remains the primary source of nutrition from 6 to 12 months. Solids slowly make up a bigger portion of the diet over that second half of the year.
This feeding timeline is one of the clearest practical markers of infancy. The transition from exclusive milk feeding to a mixed diet tracks closely with developmental milestones like sitting upright, showing interest in food, and developing the coordination to move food from a spoon to the back of the mouth.
Why the First Six Months Are a Critical Window
The infant period contains some of the highest-risk months for sleep-related dangers. SIDS (sudden infant death syndrome) peaks between 1 and 4 months of age, and 90% of all SIDS cases occur in the first six months. Sleep-related suffocation risks also concentrate in this window, with specific hazards peaking at different points: overlay deaths (when a larger person rolls onto the baby during bed-sharing) peak at 2 months, soft bedding suffocation peaks at 3 months, and wedging deaths (when a baby gets trapped between two hard surfaces) peak at 6 months.
The leading explanation for why this window is so dangerous involves three overlapping factors: an underlying vulnerability in the baby’s breathing or arousal systems, the critical early months of development when those systems are still maturing, and environmental stressors like sleeping on the stomach or overheating. Safe sleep practices are important throughout infancy, but the first half of the year is when vigilance matters most.
Quick Reference by Context
- General/CDC/WHO: Birth to 12 months (under 1 year)
- Neonatal period: Birth to 28 days (first 4 weeks)
- FDA medication labeling: 1 month to 2 years
- Product safety (CPSC): Birth to 11 months, split into three developmental stages
The most widely accepted answer is birth to 12 months. But if you’re reading a medication label or a product safety notice, check the fine print for the specific age range being used, because it may not match the everyday definition.