Was your EDD based on your LMP or the actual size of baby on a dating scan?

Mine was based on my LMP. Where I live the Midwives will only change your EDD if it is at least a week either side after a dating scan, they don't bother with just a day or two. Also the scan has to be done around 12 weeks, any later and it is deemed inaccurate as babies grow and develop at different rates.