Please help....When should I test

I'm not sure when I should test....my last period was 9 days late and only 24 hours (light) and I'm very regular....if my last period was on time then this period would start sept. 1st....but because it was late I'm not sure when it is coming....I have a very regular 28 day cycle...so do I go from the period I got then AF would be the 10 but my last period was 37 day cycle so glow is saying AF is coming a lot later....I'm so lost right now....