When am I late? 🤔

My cycles range from 27-29 days long, I am 12mo pp and on CD 30. Because I’m pp my first 2 cycles were at 37 & 35 days long so it’s thrown off my predictions. Glow has my predictions at 32 days but it’s never that late. We’re TTC & I tested 3 days ago and got a negative. I just don’t know how long to wait before i test again because I don’t know when my period should be considered late?? After glows prediction or after my actual cd average? 🤔 I don’t want to test again until I’m late. I’m tired of wasting money