Do you have any idea of when you ovulated, or when you might have conceived?

The BB due date calculator lets you change your cycle length and luteal phase (when you ovulate) if that helps at all.

Generally, I'd be going with the later date to avoid induction at the end, but I think a month is a pretty big discrepancy to have, because it means you could be way out with your 12ish week scan to check the nuchal fold. You might want to have a dating scan, or a blood test to give a better idea.

Congratulations, by the way!