Luteal Phase Calculator
Calculate your luteal phase length — the time from ovulation to the start of your next period. A normal luteal phase is 12-14 days; less than 10 days (luteal phase defect) may impair implantation and fertility.
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11-16 days: Optimal 9-10 days: Borderline Under 9 days: Likely LPD
Ready to run the numbers?
Why: Understanding luteal phase length helps identify fertility barriers.
How: Count days from ovulation to first day of period.
Run the calculator when you are ready.
Sample Scenarios
Calculation Method
Single Cycle Data
Ovulation Tracking
Optional
For informational purposes only — not medical advice. Consult a healthcare professional before acting on results.
🏥 Health Facts
Luteal phase is remarkably consistent (1-2 day variation) for each woman. Implantation window is days 6-12 post-ovulation.
— Fertility research
What is the Luteal Phase?
The luteal phase is the second half of your menstrual cycle, from ovulation to period. A healthy luteal phase (11-16 days) is essential for implantation and early pregnancy support.
How Does the Luteal Phase Work?
The corpus luteum produces progesterone during this phase. Progesterone peaks around day 7 and supports the uterine lining for implantation.
When should you calculate?
Calculate when TTC, with irregular cycles, recurrent early loss, or pre-period spotting. Track 2-3 cycles for accuracy.
Normal vs. Luteal Phase Defect
Normal: 11-16 days. LPD (<10 days) may impair implantation. Consult a provider if consistently short.
Implantation Window
Implantation typically occurs 6-12 days after ovulation. A short luteal phase may cut this window short.
Progesterone and Fertility
Progesterone supports the uterine lining. Low progesterone may shorten the luteal phase.
Lifestyle Factors
Stress, sleep, nutrition, and exercise affect luteal phase length. Vitamin B6 and C may help.
Calculation Formula
Luteal Phase Length = Period Start Date - Ovulation Date. Count days from ovulation to first day of next period.
When to Seek Help
See a provider if LP is consistently under 10 days, TTC 12+ months (6 if over 35), spotting before period, or recurrent early losses.
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