When do I test ??

Kristin • Married 2014👰🏼 miscarriage October 2014🌈baby boy December 2015💙 baby girl due July 2020💕
So I'm not sure when I should take a prego test. My last af was sept 10. Another app says af due 10/8. This app kept moving my date out and now saying 10/16.
​When should I test?! Or should I just wait and see if af comes, and if it doesn't after the 16, test?