I'm 40. I do not want to get pregnant. What r the chanced having sex using withdrawal during ovulation?

Low but not zero. Your chances of successful conception are less than if you were 25 years old due to a decrease in egg quality. However, you are still fertile until you stop having periods. Withdrawal method is not a good form of birth control because a small amount of sperm can come from the penis even before full ejaculation. Better to wear condoms especially in the first half of the cycle.