👶 Baby Age Calculator

Enter your baby's birthdate to see their exact age in weeks, months, and days as of today.

Baby's Birthdate

How each age is counted

Everything starts from whole days between the birthdate and today, both taken at midnight, so the count ticks over at the start of the day, not at the hour of birth:

days   = midnight today - midnight on the birthdate
weeks  = days / 7, rounded down, with the remainder shown as days
months = calendar difference, borrowing the previous month's
         length when today's date number is the lower one

A baby born on 15 March is 178 days old on 9 September. That is 25 weeks and 3 days, because 25 × 7 is 175. The months line reads 5 months 25 days: the month difference is six, but the 9th falls before the 15th, so a month is given back and August's 31 days make up the shortfall.

Which unit to use when

Weeks are the working unit early on - feeding, sleep and vaccination schedules are written in weeks.
Months take over from around three months, since milestone and growth references are published by month.

Because calendar months run 28 to 31 days, weeks never divide evenly into them. Eight weeks is 56 days; two calendar months is 59 to 62. The two-month date lands several days after the eight-week one, which is why appointment letters and milestone charts can look out of step.

This is chronological age only. Babies born preterm are often tracked by corrected age - chronological age minus the weeks born early - when development is compared against a reference, usually until about two years old. The tool does not adjust for that; your paediatric team decides which age applies.

Frequently asked questions

Is 8 weeks the same as 2 months old?

No. Eight weeks is 56 days, while two calendar months is 59 to 62 days depending on which months they are.

How do I work out corrected age for a premature baby?

Subtract the weeks born before 40 completed weeks from the chronological age. A baby born eight weeks early who is 20 weeks old has a corrected age of 12 weeks.

Why does the months figure not equal the days divided by 30?

Because months are counted on the calendar, not as fixed 30-day blocks. The tool matches the date number in each month and borrows the real length of the preceding month when it must.