BABY · CALCULATOR
Baby Age Calculator
How old is your baby exactly? Enter the date of birth to see months and days, weeks and days, and total days old.
Calculate your baby’s age
Examples
| Date of birth | Months + days | Weeks + days | Days old |
|---|---|---|---|
| 2026-09-10 | 1 m 0 d | 4 w 2 d | 30 |
| 2026-07-01 | 3 m 9 d | 14 w 3 d | 101 |
| 2026-04-15 | 5 m 25 d | 25 w 3 d | 178 |
| 2025-10-10 | 12 m 0 d | 52 w 1 d | 365 |
How the age is calculated
Enter the date of birth and press Calculate. Months are full calendar months since birth, and the remaining days are counted from the last monthly birthday. Weeks are total days divided by 7. “Days old” counts the day of birth as day 0.
For premature babies, doctors often use corrected age (age minus the weeks born early) for development checks. This calculator shows actual age from the date of birth.
Frequently asked questions
How do you count a baby’s age in months?
Count full months from the date of birth. A baby born on March 15 is 1 month old on April 15. If the next month has no such date, such as February 30, the month is complete on the last day of that month.
When should I switch from weeks to months?
Many parents use weeks for the first two or three months and months after that, and years after the second birthday. The calculator shows both so you can use whichever your doctor or chart asks for.
What is a baby’s “100 days” in Korea?
Koreans celebrate baek-il, the 100th day of a baby’s life, counting the day of birth as day 1. It falls on the date of birth plus 99 days.
More tools
Sources and last updated
- Month counting follows the calendar rule used in Korean law for periods ending in a month without the same date (민법 제160조).
- Ages are calculated with this device’s current date.
Last updated: · 한국어로 보기