What does it mean if you took a pregnancy test the day before your next period should start and it came out negative but the line was very faint like almost not there?

How can it be negative if there was a faint line. my period was a day late with a very faint line and im definitely pregnant u have very low HCG in ur urine at the time ur period is due if u are pregnant that's y the line is faint. Congradulations