When in your cycle to test your hormones

Some hormone tests depend on where you are in your menstrual cycle. Some don’t. The right day also depends on what you are trying to find out, so the same hormone can be timed differently for different questions.

Pick a hormone below to see what the sources say. If your lab order or your clinician gives a day, use theirs.

Pick a hormone

How to count cycle days

Cycle day 1 is the first day of your period. Day 2 is the next day, and so on. The Office on Women’s Health counts the menstrual cycle from the first day of your period up to the first day of your next one. Office on Women’s Health MedlinePlus says that for a progesterone test you may need to know the first day of your last period, so write it down before you order.

Progesterone: a week before your period, not day 21

You will often see “day 21 progesterone”. Day 21 is a week before day 28, so it lines up with “a week before your period” only if your cycle is about 28 days. The American Society for Reproductive Medicine (ASRM) says that, given the normal variation between cycles, a progesterone measurement to check for ovulation should generally be taken approximately 1 week before the next period is expected, rather than on one specific cycle day such as day 21. ASRM, 2021

A level above 3 ng/mL is, in ASRM’s words, presumptive and sufficient evidence of recent ovulation. A single value can confirm ovulation, but it can’t tell you about the quality of the luteal phase (the time after ovulation). A review of ovulation detection says the same 3 ng/mL level in the mid-luteal phase has been used to detect ovulation after the fact. Review in Bioengineering & Translational Medicine, 2017

MedlinePlus adds that progesterone changes through the menstrual cycle, and that you may need more than one test. See when to test progesterone.

FSH, estradiol and LH: it depends on the question

For ovarian reserve (the number of eggs left in the ovaries), ASRM describes “basal” FSH and estradiol, meaning early in the cycle. It says basal FSH is elevated on day 2, 3 or 4 of the cycle in women with diminished ovarian reserve. It also says FSH varies a lot between cycles and within a cycle, so one measurement has limits. ASRM, 2020

That is one question. For others, the sources we read are less specific:

• MedlinePlus says that if you have periods, you may need to be tested for FSH at a specific time in your cycle, because FSH changes through the month. It does not say which day.
• MedlinePlus says the same for LH, without a day.
• MedlinePlus’s page on estrogen tests does not give a cycle day.

So when a source doesn’t name a day, the right day is the one on your lab order or the one your clinician picks. Read more on FSH tests and estradiol tests.

AMH: timing does not matter

ASRM lists AMH as a cycle-day-independent test and says AMH stays relatively consistent within and between menstrual cycles. You can have it drawn on any day. ASRM also says AMH may be lower in women who currently use hormonal contraceptives, so tell whoever reads the result if you do. ASRM, 2020 MedlinePlus says you don’t need special preparation for an AMH test. See the AMH test.

Testosterone: time of day first

MedlinePlus says testosterone blood samples are usually taken in the morning, between 7 and 10, when levels are typically highest. Its page gives no cycle timing.

A 2025 UK guideline on evaluating androgen excess in women is more specific. It says samples should be taken in the morning, at 8 to 10 a.m., after an overnight fast, and where possible in the early follicular phase (the first part of the cycle). It says early in the cycle may not be possible when cycles are disrupted or absent. It also says testosterone does not appear to fluctuate significantly across the cycle when measured by LC-MS/MS, a mass spectrometry method. Society for Endocrinology, 2025 Labs use different methods, so your lab order may say something else.

See testosterone tests for women.

Prolactin: by the clock, not the calendar

MedlinePlus says prolactin changes through the day, so the sample is usually scheduled three to four hours after you wake up. Its page gives no cycle day. See the prolactin test.

If your cycle is irregular, absent or on birth control

If you don’t have regular periods, “day 3” may not mean much. The UK guideline above says early-cycle sampling may not be feasible when the cycle is disrupted or absent. Medicines matter too. MedlinePlus says that for estrogen and LH tests you may need to stop certain medicines or supplements first, and it says not to stop any prescription medicine unless your provider tells you to. Ask whoever ordered the test.

What the seller’s pages say

The seller’s page for its progesterone test describes progesterone as often measured about one week before the expected start of menstruation in women with regular cycles. Its AMH page says AMH does not require timing around ovulation. Its pages for estradiol and FSH say levels change through the menstrual cycle but give no day to test. For all of these, the day on your lab order is the one to follow.

If you are testing for a specific reason, such as trying to conceive, missed periods or menopause symptoms, ask the clinician who knows your history which day they want. The test finder can help you choose a test, and the fasting guide covers eating and drinking before the draw.