Question: how to calculate how many months old baby is?
Answer: 4 Weeks = a couple of days shy of 1 month (it will depend on which month your child was born in)
8 Weeks = almost a week shy of 2 months.
12 Weeks = one week shy of 3 months.
13 Weeks = 3 Months old.
16 Weeks = about a week and a half shy of 4 months old.
17.5 Weeks = 4 months old.