When to test for progesterone levels mid cycle?

Stephanie • Mother of a sweet little boy (11/13/16) and little girl (08/30/2018)! 2 MCs (12/20/2015 and 7/25/2017)
I am going to get my progesterone checked out. I heard you should do this at day 21 of a 28 day cycle. I believe my luteal phase is 11-12 days long. Any suggestions on when to test? I was thinking day 19/20.