Luteal Phase Calculator

Measure your exact luteal phase length using confirmed ovulation and subsequent period start dates.

Measure Luteal Phase Length

Enter your confirmed ovulation date (via LH test or BBT) and the first day of your next period.

Calculated on your device. Nothing is saved.

Date of LH surge + 1 day or BBT thermal shift

First day of bleeding that followed

Key Takeaway: A sufficient luteal phase (≥ 11 days) allows the blastocyst adequate time to travel down the fallopian tube and implant securely into the uterine lining.

Luteal Phase Physiology

Following ovulation, the collapsed follicle transforms into the corpus luteum, which synthesizes progesterone. Progesterone vascularizes the endometrium. If fertilization does not occur, the corpus luteum involutes after approximately 12–14 days, triggering menstruation.

When to See a Doctor

Online calculators provide general estimates based on biological averages. Consult a healthcare provider (such as an OB/GYN or general practitioner) if you notice:

  • Your periods suddenly become irregular after being consistent
  • Your cycle is consistently shorter than 21 days or longer than 35 days
  • Your period bleeding lasts longer than 7 days or is unusually heavy (soaking through a pad/tampon every hour)
  • You experience severe, debilitating pelvic pain or cramping that disrupts daily life
  • You experience bleeding between periods or after intercourse
  • You are under 35 and have been trying to conceive for 12 months (or 6 months if 35+)
  • Your period has stopped completely for 90 days or more (and you are not pregnant)
Next Logical Step

Check Your Entire Menstrual Map

View all 4 phases and hormone fluctuation curves.

Open Menstrual Cycle Calculator

Frequently Asked Questions

Evidence-based answers to common questions about your cycle and fertility.

How long should a healthy luteal phase be?

A normal luteal phase lasts between 11 and 16 days (average: 12 to 14 days). It remains relatively consistent for each individual across cycles.

What is a luteal phase defect (LPD)?

A luteal phase shorter than 10 days is clinically categorized as a short luteal phase or luteal phase defect. It may indicate inadequate progesterone production by the corpus luteum, which can prevent an embryo from successfully implanting.

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Medical & Scientific Sources

  1. American Society for Reproductive Medicine (ASRM)(2021). "Current clinical evaluation of the luteal phase: a committee opinion"
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