If you overstayed less than 6 month you will be banned to entering the US for 3 Years, and if you overstayed more than 6 Month you will be banned for 10 Years (AG)
That depends on how long you've overstayed. Overstaying by more than 6 months subjects you to an unlawful presence charge and puts you into the grounds of inadmissibility. If that's the case then you're looking of a ban from 3-5 years depending on the length of your overstay. If you've overstayed less than 6 months then I advise that you leave NOW and have your chosen petition for a K-1 visa for you. Regardless of how long you've been here, I suggest you exit the US NOW, before you're deported. You probably can get a waiver for a simple overstay if you have no criminal history, but if you're deported, then you'll throw yourself into a much larger mess.