When is baby 3months old?

[FTMF30]

E.g if a baby is born on 21st June, is the baby months old when it is 12 weeks after their date of birth? Or is it on 21st September?

I know it's a silly question but I'm actually not sure.

12 weeks isn't 3 months as there aren't 4 weeks in a month. They are 3 months on 21st September

As PP said, it will be 21st of each month. 4 weeks to estimate a month is just a guide people use as there's approximately 4 weeks in each month. If 4 weeks made a month there would only be 48 weeks in the year. For the first 6 months most things with babies are counted in weeks anyway to be honest

Thanks guys. I thought that was the case. I think my doctors must have gotten dates mixed up then.

Jabs are usually at 12 weeks rather than 3 months ..