How to track baby age in weeks
Set the birth date and the day to measure.
1
Enter the birth date
Use the date on the birth record.
2
Set the reference date
Use today or the date of an appointment.
3
Read weeks and days
The main result keeps completed weeks and adds the remaining days.
What does this tool do?
New parents are often asked for the age of a baby in weeks rather than months. This calculator counts completed weeks and leftover days, then shows the completed months and the next monthly milestone.
The Formula
Weeks = floor(Days since birth ÷ 7); days = Days since birth mod 7Frequently Asked Questions
When is a baby one month old?
On the same calendar day of the following month. The completed-months row applies that rule, including month-end clamping.
Should I use weeks or months?
Weeks are common in the first few months and months are easier later. Use one convention consistently when comparing notes with a clinician.