New pregnancy after miscarriage July 30

Sarahanne • Hi my name is sarahanne I am a 23 year old mother of 4
Omg so took this today and am very excited ! Never got a period again am suppose to get it the 17th of September so I went ahead and took 3 tests all positive.  Yay :) question :
How would I find out my due date ? Since I never had another period after I miscarried ?