Discrepancies?!

Brooklyn

Does anyone know why different apps have different dates for how far along in pregnancy I am? Just from regular glow it says 5 weeks, but glow <a href="https://play.google.com/store/apps/details?id=com.glow.android.nurture">nurture</a> says 4 weeks 6 days? Which is it? Sorry if this is a stupid question! First time mom here!