Progesterone – Day 21

Why It’s Important to Test for Progesterone (Day 21)

Progesterone is a key hormone that supports ovulation, menstrual regularity, and early pregnancy. Measuring progesterone levels around Day 21 of a typical 28-day cycle helps determine whether ovulation has occurred. Low levels may indicate problems with ovulation, which can affect fertility or menstrual health.

This test is often part of fertility investigations or used to monitor hormone balance in those experiencing irregular cycles or difficulty conceiving.

Who Should Consider Testing?

You should consider a Day 21 Progesterone test if you:

• Are trying to conceive and want to confirm ovulation
• Have irregular or absent periods
• Suspect hormone imbalances or luteal phase issues
• Experience symptoms like spotting, low mood, or fatigue in the second half of your cycle
• Are undergoing fertility treatment or hormonal investigations

When Should It Be Done?

For most people with a regular 28-day cycle, the test should be done on Day 21—about 7 days after ovulation.
If your cycle is longer or irregular, the timing should be adjusted to roughly 7 days before your next expected period, as this reflects the mid-luteal phase when progesterone peaks.