How many times you have to have sex to get pregnant?

Just one: You can get pregnant from having sex one time, even if its your first time. If you don't want to get pregnant, insist that your partner use a condom every time. Good luck!

Once: Once. That's why all women of child-bearing age should take folate (folic acid) whether planning a pregnancy or not, so they're on it for at least 3 months before conceiving to reduce the risk of neural tube defects. Avoid alcohol, tobacco & drugs if you're attempting to conceive. The fetal brain starts forming at 3 weeks & other organs soon thereafter.

Different approach: The window of conception probably extends from day 6-21 if we consider a large group of women. During these days, about 10% of women are fertile on any one day. We think sperm numbers are maximized for fertility if sex every other day. Still only about 20 of women conceive each month if they are fertile. It only takes once but only if you know the right day. Good luck.