Progesterone & Luteal Phase Calculator: 7 DPO (“Day 21”) Test Date & Ovulation Confirmation

🔬 7 DPO Progesterone & Luteal Phase Calculator

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Ovulation datePositive OPK + 1 day, BBT shift day or scan-confirmed.

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Blood draw date (if tested)

Progesterone result (optional)

Calculator Progesterone chart Luteal phase guide FAQ

7 DPO (“Day 21”) Progesterone Reference Chart (ng/mL ⇄ nmol/L)

The classic “day 21 progesterone” test only works for a 28-day cycle. The correct time is 7 days after ovulation (or 7 days before the expected period). In a 35-day cycle that is about cycle day 28.

Mid-luteal progesterone	nmol/L	Natural cycle	Letrozole / Clomid cycle
< 3 ng/mL	< 9.5	No ovulation	No ovulation — dose may need adjusting
3 – 10 ng/mL	9.5 – 31.8	Ovulated; suboptimal / check timing	Ovulated; suboptimal
> 10 ng/mL	> 31.8	Good ovulatory level	Ovulated
> 15 ng/mL	> 47.7	Strong	Good level for medicated cycles

Conversion: 1 ng/mL = 3.18 nmol/L. NICE (UK) uses > 30 nmol/L as confirmation of ovulation.

Luteal Phase Length: Normal, Short & What to Do

Luteal phase	Meaning
< 10 days	Short — possible luteal phase deficiency
10 – 11 days	Borderline
12 – 16 days	Normal
> 16 days without a period	Possible pregnancy — test

Count from the day after ovulation up to the day before your next period.
Progesterone is released in pulses, so a single “low” value can be misleading; one repeat test is reasonable.
ASRM states there is no reliable test for luteal phase deficiency — treat the cause (thyroid, prolactin, ovulation problems) where found.

Frequently Asked Questions

When should I test progesterone to confirm ovulation?

Test 7 days after ovulation (7 DPO), which is cycle day 21 only in a 28-day cycle. In a 32-day cycle, for example, test around day 25.

What progesterone level confirms ovulation?

A level above 3 ng/mL (about 10 nmol/L) shows ovulation occurred; above 10 ng/mL (30 nmol/L) is considered a good natural-cycle level.

What is a short luteal phase?

A luteal phase shorter than 10 days. It may reduce the time available for implantation and is worth discussing with a doctor, especially with other cycle problems.

Can low progesterone cause miscarriage?

Very low progesterone can be associated with pregnancy loss, but often it reflects a pregnancy that is not progressing rather than the cause. Progesterone treatment may help women with bleeding and previous miscarriages (PRISM trial).

How do I convert progesterone from nmol/L to ng/mL?

Divide nmol/L by 3.18. For example, 32 nmol/L ≈ 10 ng/mL.

⚠️ Official Medical Disclaimer

This calculator is for informational and educational purposes only. It produces mathematical estimates based on published clinical literature (ACOG, ASRM, ESHRE, NICE, WHO, NEJM) and is not a medical diagnosis, treatment plan, or method of contraception.

Every body and every treatment cycle is different. Always discuss your results with a qualified OB-GYN, reproductive endocrinologist, or fertility specialist before making any medical decision. Seek urgent care for heavy bleeding, severe one-sided pain, fainting, or fever.

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