👶 Baby Age Calculator
Enter your baby's date of birth to see how old they are in days, weeks and months — plus milestone dates like the 100th day and first birthday.
Milestone dates (100th day, birthdays)
Month-by-month calendar (1–24 months)
How to use the baby age calculator
Enter your baby's date of birth and you'll see their age today in days, weeks and months. Below are milestone dates — the 50th and 100th days, 6 months, the first and second birthdays, 1,000 days — with a countdown, plus the date each month from 1 to 24 begins. The next milestone and the current month are highlighted. If your baby was born early, enter the weeks of pregnancy at birth to see their corrected age too.
How baby age is calculated
- Months A month is complete each time the birth day-of-month comes around: a baby born March 15 is 1 month old on April 15 and 2 months on May 15. For birthdays like the 31st, the last day of shorter months counts.
- Weeks
days old ÷ 7— the quotient is weeks and the remainder is days. Pediatric and feeding guides often use weeks until about 3 months. - First birthday The same date one year later — not a day count.
- Corrected age
actual age − (40 weeks − weeks at birth), used for babies born before 37 weeks.
The 100th day (baek-il) — why is it 99 days later?
In Korea, a baby's 100th day (baek-il, 백일) is celebrated with a small feast of rice cakes and photos, a tradition from times when surviving the first 100 days was a milestone. Koreans count the day of birth as day 1, so the 100th day is the birth date + 99 days — a baby born January 1 has their 100th day on April 10 (in a common year). The first birthday (dol, 돌) is an even bigger celebration. "Days old" in medical records usually counts the birth day as day 0, so both numbers are shown.
What is corrected age?
Babies born before their due date may reach milestones later than babies of the same birth age. To account for this, doctors often use corrected (adjusted) age — age counted from the original due date. For example, a baby born at 32 weeks who is 6 months old has a corrected age of about 4 months (8 weeks subtracted). Corrected age is generally used until around age 2; your pediatrician will tell you when to stop.
Checkups and vaccines
Well-baby visits and vaccines are scheduled by age (in the US, commonly at 3–5 days, 1, 2, 4, 6, 9, 12, 15, 18 and 24 months). Schedules change and vary by country, so check with your pediatrician or your national immunization schedule (CDC in the US, KDCA in Korea).
This is a date calculator. For questions about growth, development, vaccines or checkups, follow your pediatrician and official health guidance.