How Old Is My Baby?
How this is calculated
This calculator compares your child's date of birth to today's date and works out the difference in calendar terms — full years, then leftover months, using the same logic as counting on your fingers from one birthday to the next. It also converts the total elapsed time into whole weeks and whole days, which is handy in the newborn and infant stage when "months old" isn't precise enough and parents, pediatricians and baby milestone charts often talk in weeks instead.
The "next birthday" countdown finds the closest upcoming anniversary of the birth date (this year's if it hasn't happened yet, otherwise next year's) and counts the days remaining, along with the age your child will be turning.
These same building blocks — total elapsed days, weeks, months and years — are also what pediatric growth charts and developmental milestone checklists use to plot where a child is expected to be at a given point, which is why knowing an exact age in weeks or months (not just "almost 2") is often more useful in the early years than it might seem.
Common edge cases & things to know
Children born on February 29 in a leap year technically only have a birthday on the calendar every four years — most families and this calculator treat February 28 (or March 1) as the "birthday" in non-leap years for the purposes of counting age and next-birthday countdowns.
If your baby was born premature, you may hear your pediatrician refer to corrected (or adjusted) age — age counted from the original due date rather than the actual birth date. This is commonly used for growth and developmental comparisons up until around 2 years old, since it gives a fairer picture of a preemie's progress. This calculator shows chronological age (from actual birth date); for corrected age, you can enter the due date instead if that's the number your care team wants you to track.
Dates are compared using your device's local time zone, so if you're calculating right around midnight the "days old" figure may shift by one depending on when exactly you check.
Age is also expressed differently depending on culture and context — some countries traditionally count age from conception or round up at the new year rather than the Western "years since birth" convention used here. If you're comparing ages across families or documents from different regions, it's worth confirming which convention is in use.
Sources
General age-tracking and developmental milestone guidance referenced from the Centers for Disease Control and Prevention (CDC) and HealthyChildren.org, the parent-facing site of the American Academy of Pediatrics.