Baby Age in Weeks Calculator

About this calculator

In a baby's first year, age is most meaningfully tracked in weeks rather than months, since growth, feeding schedules, sleep patterns, and developmental milestones all shift noticeably from one week to the next in a way monthly tracking glosses over. This calculator works out a baby's age in weeks plus days, in months, and as a total day count from the birth date to any chosen as-of date.

Pediatric guidance — like well-baby visit schedules, vaccination timing, and developmental milestone checklists — is frequently expressed in weeks of age, especially in the newborn period. New parents and caregivers use a week-based age calculator to stay on top of that timeline and to answer the very common question of exactly how old a baby is on a given day.