Newborn Essentials: Age, Growth & First Months
The first year is mostly about three numbers: how old your baby is in weeks and months, how they're growing, and how much they're sleeping. The right combination of tools answers the questions you actually get asked at every pediatric visit.
Last reviewed: June 25, 2026
Calculators in this topic
Free, evidence-based tools — no signup, no data stored.
Convert your baby's date of birth to exact age in years, months, weeks, and days. Perfect for milestones, vaccinations, and pediatric visits.
Calculate adjusted (corrected) age for babies born preterm. Used to interpret growth, milestones, and screening tools accurately until 24 months.
Plot your baby's weight and length against WHO Child Growth Standards. Get percentiles and z-scores instantly.
How much sleep does your child need? Get age-based total sleep hours, suggested bedtimes, and nap patterns based on AAP/AASM guidance.
Start with exact age
A baby age calculator gives you weeks, months, and days — the units pediatricians, vaccine schedules, and milestone charts all use.
Then layer growth and sleep
Plot weight, length, and head circumference percentiles at each visit, and pair them with an age-appropriate sleep total. Anything that drifts off-trend is worth a conversation with your pediatrician.
Explore related topics
Why corrected age matters for premature infants, how to calculate it, and how to apply it to growth charts and developmental screening.
How pediatricians read growth charts, when a percentile change matters, and how BMI is interpreted for children differently than for adults.
Age-appropriate sleep totals, nap transitions, and how sleep links to development and growth in the first six years.