5weeks or 6weeks

1st day of last period is on 8th jan 2023 . Kalau refer to asianparent app. Baru 5w1d tapi kalau refer apps lain dah 6w1d. So sebenarnya 5w or 6w ye ? Anyone tau calculate . Or anyone yg tarikh last period tu sama ? So korang pon baru 5w depends on this apps ke ?