I have a date based on my 26 day cycle. I was going to go with a date based on a 28 day cycle but given I have an IM we decided to go with the "right" date so we know where abouts baby should be at and just see what happens.

Both my children have measured 6 days earlier at their scans but I've always stuck with the date based on my cycle- buys more "overdue" time anyway.