Why does glow do that

Jordyn
When you press the "period is late" button why does it push your period out for 5 days, where does it get that estimate from? We have been babydancin all dang month im exhausted lol... I was due on 23rd and got positive opks for 3 days starting on 19th till 22nd and i tested hcg yesterday it was negative:( so what now