I fell pregnant with Harry due to anti-depressants meds clash so didn't know I was pregnant but going by my LMP he was due 31st Oct. My scan put me forward by one week, to 24th Oct.
When he eventually came (induced) I was 17 days over, but really, when I think about it now it's only 10 days, looking at it from the original dates.
This time we said 8th April based on what we know (OV etc), and our scan at 7 weeks and 11 weeks said 8th; NHS scan at 12 wks said 5th, midwife said we could choose so we went with the latest date to give us a bit longer to avoid being induced, if it comes to that.