I'am 20 weeks pregnant sunday will be 21 how many month is that please?

4 weeks per month: Obgyn's discuss pregnancy dates in terms of weeks instead of months. There are 4 weeks in each months. If you prefer to think in months then simply divide the number of weeks by four.

Almost 5 months: You will have likely 19 weeks more to 40 weeks.

Term = 40 wks: It is estimated that the full-term pregnancy is about 40 wks, so you are a bit more than half-way there...Congrats. In term of months, 4 wks= 28 days so if counting 30 days/month, 21 wks is just shy of 5 months. Consult doc. Good luck.