Age calculator of baby
Enter your baby’s birth date to see how old they are today, in months and days and in weeks and days. If your baby was born early, add the due date to see the corrected age too.
- Age
- 3 months, 8 days
A baby born on June 22, 2026 is 3 months, 8 days old on September 30, 2026.
- In weeks
- 14 weeks, 2 days
- Days old
- 100
Answer for the example date Wednesday, September 30, 2026. It changes to today's date when the page loads.
Age: 3 months, 8 days. A baby born on June 22, 2026 is 3 months, 8 days old on September 30, 2026.
Where are the dates on the calendar?
How to calculate
Works out how old a baby is from the birth date, in months and days and in weeks and days, and the corrected age of a baby born before the due date.
Example with the default inputs (Birth date June 22, 2026, Age on September 30, 2026) on the example date Wednesday, September 30, 2026: A baby born on June 22, 2026 is 3 months, 8 days old on September 30, 2026.
Method: age = the whole years, months, and days from the birth date to the age-on date; corrected age = the same from the due date (the age less the weeks born early)
- Dates are whole calendar days with no time of day; the day of birth is day 0.
- Months are calendar months from the birth date; a day that a month does not have moves to its last day.
- Corrected age (AAP) counts from the due date. Use it for a baby born early, for the first 2 years.
- The age-on date is today unless you change it; the page reads today’s date from your device when it loads.
Worked examples
Each example is checked against the calculator on every build.
- Birth date 2026-06-22, Age on 2026-09-30 gives Age 3 months, 8 days, In weeks 14 weeks, 2 days, Days old 100.Source: Julian Day numbers (Meeus, Astronomical Algorithms, 1991, chapter 7): JD 2461313.5 − JD 2461213.5 = 100 days
- Birth date 2026-01-01, Age on 2026-04-23, Due date (if born early) 2026-02-26 gives In weeks 16 weeks, Born early by 8 weeks, Corrected age in weeks 8 weeks, Corrected age 1 month, 28 days.Source: American Academy of Pediatrics, HealthyChildren.org, Corrected Age For Preemies: corrected age = age in weeks − weeks born early (https://www.healthychildren.org/English/ages-stages/baby/preemie/Pages/Corrected-Age-For-Preemies.aspx)
- Birth date 2026-09-01, Age on 2026-09-30, Due date (if born early) 2026-10-20 gives In weeks 4 weeks, 1 day, Born early by 7 weeks, Days to the due date 20.
- Birth date 2024-02-29, Age on 2026-02-28 gives Age 2 years, Days old 730.Source: Gregorian leap-year rule (ISO 8601)
How it works
Dates are whole calendar days in the Gregorian calendar, with no time of day. The day of birth is day 0, so a baby is 1 day old the next day. Dates from January 1, 1900 to December 31, 2400 are accepted. A birth date after the age-on date has no answer.
- Age (years, months, and days): from the birth date, the most whole years Y such that the birth date plus Y years is not after the age-on date; then the most whole months M such that the birth date plus Y years and M months is not after it; then the days left. A day that a month does not have moves to the month’s last day (a baby born on January 31 is 1 month old on February 28, or 29 in a leap year).
- Days old = age-on date − birth date, in whole days.
- In weeks = days old ÷ 7 rounded down, and the days left (0 to 6).
Corrected age, for a baby born before the due date (American Academy of Pediatrics):
- Born early by = due date − birth date, as whole weeks and days. The due date must be after the birth date and at most 20 weeks (140 days) after it; otherwise there is no answer.
- Corrected age = the age counted from the due date instead of the birth date: whole years, months, and days from the due date to the age-on date, by the same rule as the age. Corrected age in weeks = (age-on date − due date) ÷ 7 rounded down, and the days left. This is the age in days less the days born early.
- When the age-on date is before the due date, there is no corrected age yet; Days to the due date = due date − age-on date.
The age-on date starts as today and the birth date as 100 days before today. The page was built on one day and may be opened on another: the built page shows the dates of its build day, and your browser replaces them with yours as soon as the page loads.
Worked examples by hand
Born June 22, 2026; age on September 30, 2026. June 22 plus 3 months is September 22, and 8 more days is September 30: 3 months and 8 days. In days: 8 (to June 30) + 31 + 31 + 30 = 100 days, and 100 = 14 × 7 + 2, so 14 weeks and 2 days.
Born 8 weeks early (the American Academy of Pediatrics example). Born January 1, 2026, due February 26, 2026 (56 days = 8 weeks later, so born at 32 weeks). On April 23, 2026 the baby is 112 days = 16 weeks old. Corrected age: from February 26 to April 23 is 56 days = 8 weeks, which is 16 − 8. In months: February 26 plus 1 month is March 26, and 28 more days is April 23: 1 month and 28 days.
Before the due date. Born September 1, 2026, due October 20, 2026: born early by 49 days = 7 weeks. On September 30 the baby is 29 days = 4 weeks and 1 day old, and the due date is 20 days away, so there is no corrected age yet.
Born February 29, 2024; age on February 28, 2026. 2026 is a common year, so the second birthday falls on February 28: 2 years exactly, 365 + 365 = 730 days.
Other questions people ask
How do I work out my baby’s age in weeks?
Count the days from the birth date to today and divide by 7. The whole number is the weeks and the remainder is the days. A baby born 100 days ago is 14 weeks and 2 days old, because 100 = 14 × 7 + 2.
How do I work out my baby’s age in months?
Count calendar months from the birth date: the baby turns 1 month old on the same day of the next month. A baby born on June 22 is 3 months old on September 22, and 3 months and 8 days old on September 30.
What is corrected age?
Corrected age (also called adjusted age) is the age of a baby born early counted from the due date instead of the birth date. The American Academy of Pediatrics says to take the baby’s age in weeks and subtract the weeks born early: a baby born at 32 weeks is 8 weeks early, so at 16 weeks old the corrected age is 8 weeks.
How long should I use corrected age?
The American Academy of Pediatrics suggests using corrected age for growth and developmental milestones in the first 2 years. Vaccines are different: the CDC says babies born early get them at the same age from birth as other babies, not by corrected age. Ask your pediatrician if you are unsure.
What if today is before my baby’s due date?
Then the corrected age has not started yet, and the calculator shows the days left until the due date instead.
What happens with a February 29 birthday?
In a common year the birthday falls on February 28. A baby born on February 29, 2024 is 2 years old on February 28, 2026.
Why does the age change when I open the page on another day?
The age-on date starts as today, read from your device when the page loads. The page itself was built on an earlier day, so it shows that day’s age until your browser works out today’s. Pick an age-on date for a fixed answer.