depends how long since your last period. if you just missed your period, then you're about 4 weeks. But some women can still get what they think is a period and actually be pregnant, so you would need an ultrasound to confirm which most doctors wont due till 8 weeks, which they base off of your last period. With a positive test, time to call and schedule an apt with your obgyn! Congrats! :)
Google pregnancy calculator and that's one way other way oohs check with doctor, good luck