Are pregmate tests reliable?

Ashley • Dog mom 🐾 teacher 👩‍🏫 writer 📖 pcos

So im four days late on my period. I'm usint pregmate tests. I took one yesterday morning and one after work today, both are negative. I stopped cramping yesterday, but still no period. I'm slightly nauseous. I'm just curious on how reliable are the tests? They are red dye.