My monthly/possible pregnancy

Hailey
How come if your period is late glow continuously backs it up by two days? I'm getting a pregnancy test today but I had my period on the 14th last month and this month it was expected on the 14th too but glow predicted the 16th. When I entered that I hadn't got my period today it just pushed two days to the 18th and then again until the 20th. Just curious.
UPDATE/ I decided to test! :) I'm so happy right now!