That depends on you. Your method of birth control, lifestyle, and genes all play a role in how long it will take to get pregnant after quitting birth control. Quitting barrier methods of birth control—such as condoms or a diaphragm—have no downtime to getting pregnant. If there are no fertility issues to getting pregnant, the egg is capable of being fertilized and pregnancy can occur at the next ovulation cycle.
For birth control that has hormones, it is a different story. Most women can get pregnant within weeks to months after they stop hormonal birth control methods depending on the half-life of such birth control as pills, patches, vaginal rings, depot injections or intrauterine devices(IUD).