How was your due date calculated?

Angel

So today is my due date based on my LMP. However, since I had an IUD at the time I discovered I was pregnant, I got two very early sonograms and my due date was recalculated based on the size of my gestational sac. First sonogram there was no sac. A few days later it was there! So we caught it at the very beginning. May 25th was estimated as my due date instead. I cant help but wonder if my due date is a closer date estimate than women who go by their LMP. If it hadn't been for my IUD and those early sonograms we would be hoping for a baby by today and would think I was late should baby come sometime next week.

How was your date calculated and if you had baby already, how far along were you?