Agree with the comment above. Only February is exactly 4 weeks, the rest of the months are longer so saying a month for every 4 weeks would put your baby at a year old when they're only about 11 months
Calculation is like this : 9 months = 40 weeks, therefore 1 month = 4.5 weeks as 1 month has 30 or 31 days so 7 days per week. 31 days divided by 7 days it's seen as 4.5. At 18weeks your baby was 4 months. Hope this helps😇
4 months last week on the 18/7. Always go by the date they were born per month. If you do it by weeks they’ll be 1 before or after the 18th. Not all months have 4 weeks in them etc so always go by the date they were born!