Ok moms help.. Lol I'm due the 31 st ( probably won't make it but edd is 31 st ) and websites are…

Ok moms help.. Lol I'm due the 31 st ( probably won't make it but edd is 31 st ) and websites are showing I conceived around the first day of feb which doesn't really add up to 9 months I wouldn't think but Iv seen it multiple times. Anyone wanna explain how all that works? Just a curious first time mom.. And go! 😊