Confused.. am I 4 weeks 5 days or 4 weeks 6 days

ka

My baby centre app says I’m 4 weeks 6 days

My last period started April 29th

I think that means Monday is 5 weeks

So is it like

4 weeks is day one of that week

And the second day is 4 weeks 1 day and the last day would be 4 weeks 6 days

Or does it go from 4 weeks 1 day being the first day of the week and up to 4 weeks 7 days as the last day

I know it’s not THAT important but i just want to understand it so that I know