How are Weeks Counted? Baby app confusion 😧

The Bump, What to Expect and Ovia all say I'm 5 weeks 7 days today but my actual period tracker and favorite app Glow says im 6 weeks today which totally skipped the 5 wk 7 day.

Ladies how is it tracked is the 7th day real? I tend to rely more on this app because its based off my af info I've tracked for months using Glow.

I was told at 5 wk 4 dys I had pregnancy Undisclosed Location they wanted me back in 48 hours but I fig I would go when I hit 6 weeks since im sure my lil poptart will show.