Baby age calculator

Her exact age in days, weeks, months and years, and when her next month birthdays fall. Born before 37 weeks? Use the corrected age calculator.

Short answer: A baby's age in months is counted in calendar months from her date of birth. Born on March 15, she turns 1 month on April 15 and 2 months on May 15. Born on the 29th, 30th or 31st, she turns a month older on the last day of any shorter month. Age in weeks is simply her age in days divided by seven.

Nothing you enter is stored or sent anywhere. Days are counted on your device's local calendar, so the result doesn't shift with time zones.

In Chapter 4 of Big Bang Baby I write that the range of normal is astonishingly wide: your baby's age tells you where she is on the calendar, and for any particular skill it's a landmark, not a deadline. Here's how wide that range really is; the full why is in Chapter 4. Read the Introduction free.

Sources

Big Bang Baby, Chapter 4, "Cooling and Differentiation": the range of normal; expected ages as landmarks, not deadlines.
American Academy of Pediatrics, HealthyChildren.org: Corrected Age For Preemies (corrected age during the first two years).
Centers for Disease Control and Prevention: Preterm Birth (before 37 completed weeks of pregnancy).