Nurture admin please explain why the app is 1 week behind?

I input all the same info in nurture and other apps and even online calculators.

nurture says I'm 1 week less than all the others. What is right?

The first day of my LMP was Jan 7, I 100% ovulated on Jan 23rd (cycle day 17).

That would make me 5 weeks not 4......

According to my ovulation I should be 5w2d today.

First ultrasound is Thursday (feb 18) and they will figure it out but I've has loses... so if it's too early and they see nothing I will be devestated.

Thanks!