The Playbook

Baby age calculator

Enter the birth date for your baby's age in days, weeks and months, the next month-birthday, and upcoming checkups. Born early? Add the due date for corrected age.

Enter a birth date to see the age in days, weeks and months.

By the Guide to Fatherhood editorial team. Last reviewed .

Checked against guidance from organizations like the AAP, CDC, ACOG and NHS (linked below). This is general information, not medical advice. Read our medical disclaimer.

What the calculator shows

  • Exact age in months and days, weeks and days, and total days. The birth day is day 1, which is how hospitals and baby apps usually count.
  • Corrected age if you add a due date at least three weeks after the birth date.
  • The next month-birthday and the first birthday, with countdowns.
  • Upcoming well-child checkups based on the AAP’s Bright Futures schedule.
  • A link to the matching month-by-month dad guide, so you know what is typical right now and what to do about it.

Share the link and it opens with the same birth date. Handy for grandparents who keep asking.

Why corrected age matters

A baby born at 32 weeks is eight weeks early. At four months old, they are developmentally closer to a two-month-old, and that is completely expected. The AAP recommends judging milestones by corrected age, usually until about age 2, when most preemies have caught up.

If your baby spent time in the NICU, your pediatrician and follow-up clinic will tell you which age to use for what. Vaccines generally follow chronological age; development checks use corrected age.

Milestones: use them as a conversation starter

The CDC’s milestone checklists list skills most babies show by 2, 4, 6, 9 and 12 months, such as smiling at people by 2 months or sitting without support by 9 months. They are designed to help you notice and ask, not to grade your baby. If something seems off, or your gut is bugging you, mention it at the next checkup or call sooner. Acting early is always better than waiting to see.

Frequently asked questions

How do you calculate a baby's age in months?

Count full calendar months from the birth date, then the leftover days. A baby born on January 15 turns 3 months old on April 15. For month-end birthdays, we use the last day of shorter months (a January 31 baby is 1 month old on February 28 or 29).

What is corrected age?

For babies born before 37 weeks, corrected age (also called adjusted age) is the age they would be if born on the due date: chronological age minus the weeks born early. Pediatricians often use it to judge development and growth until about age 2.

What are the well-child checkups in the first year?

The AAP's Bright Futures schedule includes a newborn visit at 3 to 5 days, then visits at 1, 2, 4, 6, 9 and 12 months. Your pediatrician may add visits, such as a weight check in the first week or two.

Which week of life is my baby in?

The calculator shows the day number (birth day is day 1) and the age in completed weeks and days.

Sources

  1. Recommendations for Preventive Pediatric Health Care (Periodicity Schedule), American Academy of Pediatrics, Bright Futures
  2. Corrected Age For Preemies, American Academy of Pediatrics (HealthyChildren.org)
  3. CDC's Developmental Milestones, Centers for Disease Control and Prevention

We link to the original source for every medical and safety claim. Guidance changes; if a source has been updated since our last review, the source wins. How we research.