I am not sure how long deprovera is in your system, but the pill usually takes 3 months after you stop taking them. So how long is deprovera supposed to prevent pregnancy? I would add 3 months. Then like the other poster said, it can vary how long it will take you to get pregnant. It took me 6 months after taking the pill with my first and 9 months for the second. So even the same person can have different results.