What are the chances of getting pregnant on the pill?

According to the Palo Alto Medical Foundation, the chances of a woman getting pregnant while she is on the pill are about 5 percent if she uses the pill typically, and about 0.1 percent if she follows the guidelines perfectly. Women must take birth control pills daily and as prescribed to best reduce their chances of pregnancy.

Women must take the pills in the correct order. Waiting even a half-day later than required increases the chances of pregnancy if the pills are of an extremely low dosage. Skipping two or more pills in a row or taking them too late during a menstrual cycle also increase the chance of pregnancy, as the Association of Reproductive Health Professionals points out.