When to Test Hormones: The Best Days of Your Cycle for Accurate Results

You finally convince your doctor to run hormone tests - but they draw your blood on a random day, and your results come back "normal." Sound familiar?

Here's what most women don't know: hormone testing timing matters enormously. Test progesterone on Day 5 of your cycle and it will always be low - that's not a problem, that's physiology. Test cortisol in the afternoon instead of morning and you might look like you have adrenal insufficiency when you don't.

Understanding when to test each hormone is the difference between useful, actionable results and completely meaningless numbers.

Why Timing Matters: The Menstrual Cycle

Women's hormones are designed to fluctuate - that's the whole point of a menstrual cycle. According to research published in Endocrine Reviews, hormone levels can vary by 10-fold or more depending on cycle phase.

The four phases of your cycle:

• Menstrual Phase (Days 1-5): Hormone levels are at their lowest
• Follicular Phase (Days 1-14): Estrogen gradually rises as follicles develop
• Ovulation (Day 14-ish): LH surges, estrogen peaks, egg is released
• Luteal Phase (Days 15-28): Progesterone rises and peaks around Day 21

Testing the same hormone on Day 3 versus Day 21 can give completely different - and equally valid - results. The question is what you're trying to learn.

Hormone-by-Hormone Timing Guide

FSH (Follicle Stimulating Hormone)

When to test: Day 2-4 of your cycle (early follicular phase)

Why: FSH is tested at baseline to assess ovarian reserve and function. According to Fertility and Sterility guidelines, Day 3 FSH is a standard part of fertility evaluation. Elevated FSH at this point suggests diminished ovarian reserve.

What it tells you:

• Ovarian reserve and egg supply
• Whether you're approaching perimenopause
• Potential fertility challenges

Reference ranges (Day 3):

• Normal: 3-10 mIU/mL
• Borderline: 10-15 mIU/mL
• Elevated: >15 mIU/mL (suggests diminished ovarian reserve)

LH (Luteinizing Hormone)

When to test: Day 2-4 for baseline, or mid-cycle to confirm ovulation

Why: Baseline LH helps diagnose PCOS (often elevated with high LH:FSH ratio). Mid-cycle LH surge confirms ovulation is occurring.

What it tells you:

• LH:FSH ratio elevated in PCOS
• LH surge indicates ovulation (useful when TTC)
• High baseline LH may indicate pituitary or ovarian issues

Estradiol (E2)

When to test: Day 2-4 for baseline; can also test mid-cycle

Why: Day 3 estradiol helps interpret FSH results. According to research in reproductive endocrinology, elevated early-cycle estradiol (>80 pg/mL) can artificially suppress FSH, masking diminished ovarian reserve.

Reference ranges:

• Day 3: 25-75 pg/mL (optimal for ovarian reserve assessment)
• Mid-cycle peak: 200-400 pg/mL
• Luteal phase: 40-200 pg/mL

Progesterone

When to test: 7 days after ovulation (Day 21 in a 28-day cycle)

Why: Progesterone is only produced after ovulation by the corpus luteum. Testing at any other time will show low levels regardless of whether you ovulated. A Cochrane review confirms that mid-luteal progesterone is the standard for confirming ovulation.

Reference ranges (mid-luteal):

• Ovulation confirmed: >3 ng/mL
• Good luteal function: 10-20 ng/mL
• Optimal for conception: >15 ng/mL

Low progesterone can indicate:

• Anovulation (didn't ovulate)
• Luteal phase defect
• Early pregnancy loss risk
• Progesterone deficiency symptoms (PMS, anxiety, insomnia)

Testosterone (Total and Free)

When to test: Day 2-5 (early follicular) is ideal, but any day is acceptable

Why: Unlike estrogen and progesterone, testosterone doesn't fluctuate dramatically with your cycle. However, it's slightly higher around ovulation. For consistency, early follicular is preferred.

Best tested in the morning - testosterone has a diurnal rhythm with higher levels in AM.

What it tells you:

• PCOS (often elevated total testosterone)
• Low libido, fatigue, muscle weakness (may be low testosterone)
• Hirsutism and acne (elevated androgens)

DHEA-S

When to test: Any day - does not fluctuate with menstrual cycle

Why: DHEA-S is an adrenal androgen with stable levels. It's useful for evaluating androgen excess alongside testosterone.

What it tells you:

• Adrenal androgen production
• Source of elevated androgens (adrenal vs. ovarian)
• Adrenal fatigue (if very low)

AMH (Anti-Müllerian Hormone)

When to test: Any day - does not fluctuate with menstrual cycle

Why: AMH reflects ovarian reserve (egg supply) and doesn't change significantly during your cycle. According to research in Human Reproduction Update, AMH is the most reliable marker for ovarian reserve.

Reference ranges by age:

• 25-30 years: 3.0-7.0 ng/mL typical
• 30-35 years: 2.0-5.0 ng/mL typical
• 35-40 years: 1.0-3.0 ng/mL typical
• <1.0 ng/mL at any age suggests diminished ovarian reserve

Thyroid Hormones (TSH, Free T3, Free T4)

When to test: Any day of your cycle - thyroid doesn't follow menstrual rhythm

Why: Thyroid hormones follow a circadian rhythm (slightly higher in morning) but don't fluctuate with your menstrual cycle. However, they interact significantly with reproductive hormones.

According to the American Thyroid Association, thyroid dysfunction affects fertility, menstrual regularity, and pregnancy outcomes. Every woman with cycle irregularities should have a complete thyroid panel.

Best practices:

• Test in the morning (TSH is highest in early AM)
• Test before taking thyroid medication
• Include Free T3, Free T4, and antibodies - not just TSH

Cortisol

When to test: Morning (7-9am) for blood; 4-point saliva test for full picture

Why: Cortisol follows a strong circadian rhythm, peaking within 30 minutes of waking and declining throughout the day. A 2009 study in Psychoneuroendocrinology confirmed the importance of standardized timing for cortisol measurement.

Reference ranges (morning blood):

• Normal: 10-20 mcg/dL (varies by lab)
• <5 mcg/dL: Possible adrenal insufficiency
• >25 mcg/dL: Possible Cushing's or severe stress

Special Situations

Irregular Cycles

If your cycles are irregular, timing becomes tricky:

• For baseline hormones (FSH, LH, E2): Wait for a period and test Day 2-4
• For progesterone: Use ovulation predictor kits to detect LH surge, then test 7 days later
• If no periods: Test anytime - irregular cycles themselves are diagnostic

On Birth Control

Hormonal contraception (pill, patch, ring, hormonal IUD, implant) suppresses your natural hormone production. Testing while on birth control will not show your true levels.

To get accurate results:

• Discontinue hormonal birth control for at least 3 months
• Wait for at least 2 natural cycles to establish rhythm
• Some experts recommend 6 months for full recovery

Exception: AMH is not affected by birth control and can be tested anytime.

Perimenopause

During perimenopause, hormone levels become erratic. According to research in the Journal of Clinical Endocrinology & Metabolism, testing during this transition may show wide variability.

Tips for perimenopausal testing:

• Track symptoms alongside lab work
• Test multiple times over months to see patterns
• Elevated FSH >25 mIU/mL suggests approaching menopause
• Symptoms may not correlate perfectly with levels

Common Testing Mistakes to Avoid

1. Testing progesterone on a random day - Will almost always be low if not Day 21
2. Testing cortisol in the afternoon - Will appear falsely low
3. Only testing TSH for thyroid - Misses T3/T4 problems and autoimmunity
4. Testing while on birth control - Doesn't reflect true hormone production
5. Assuming Day 21 works for everyone - Only accurate for 28-day cycles
6. Not repeating abnormal results - One test can be a fluke; patterns matter

The Bottom Line

Hormone testing is only as good as its timing. A "normal" progesterone on Day 10 means nothing; a "low" cortisol at 4pm doesn't indicate adrenal problems. Understanding when to test each hormone ensures you get results that actually mean something.

Before your next hormone panel, know exactly which tests need specific timing - and communicate with your provider about scheduling your blood draw accordingly. Your health decisions depend on accurate data.