What is the probability of pregnancy 8 days before ovulation? i took a plan b on the 4th day but it was the day before i even reached my fertile window?

Pregnancy has been documented from exposure on any day of a woman's cycle, including during menses. The concept of a fertile window is good if trying to time sex to improve chances of pregnancy, but not so good if trying to avoid it. Plan B taken within 48-72 hours of exposure usually prevents pregnancy, after 4 days, maybe not.

Agree with Dr. Ferguson. Pregnancy can occur from sex on any and all days of the cycle. Plan B is about 95% effective if taken within 72 hours of sex. If you do not wish to be pregnant, use contraception all the time, every time. You may consider implanted contraceptive, or IUD. Practice safe sex : https://www.hopkinsmedicine.org/health/wellness-and-prevention/safer-sex-guidelines Get HPV vaccine