date leeway on day 21 test

[yellowflowers]

Anyone know whether the day 21 progesterone test must be bang on 7 days after ovulation or can be a few days either side and if it can be either side, how many days can it be?
Thanks

Hi yellow

Didn't want to leave your post unanswered. My doc explained to me that the "day 21" test should be about half way through your luteal phase. So it would only be 7 dpo if you have a 14 day luteal phase ("day 21" is just shorthand for this as it's based on that mythical woman with the 28 day cycle who ovulates on day 14!).

I was also told to try and get it as close as possible mid-luteal phase as too early and your prog levels may not be high enough; too late and your levels may have started to drop. Both being too early or being too late would give misleading results.

HTH