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FREE CLINICAL TOOL · WILCOX / ASRM · LH SURGE + CYCLE PHASE · NOT FOR CONTRACEPTION

Ovulation & Fertile
Window Calculator.

LH surge + cycle-phase dual engine. Day-by-day fertility probability from clinical evidence — with PCOS-aware confidence scoring and conception-window guidance.

Wilcox et al. NEJM · ASRM 2022
LH Surge + Calendar Dual Engine
PCOS-Aware Confidence Scoring
⚕️ Not for contraception

Enter Your Cycle Details

Calendar + LH surge model · Wilcox / ASRM · PCOS-aware

First Day of Last Period (LMP) * Day 1 of your most recent menstrual cycle — the first day of full bleeding (spotting doesn't count). This anchors all cycle-day calculations.
Usual Cycle Length * Count from Day 1 of one period to Day 1 of the next. Average of 3–6 cycles gives the best estimate. Typical range: 21–40 days. Average: 28 days.
Cycle regularity
LH Surge Date (optional — significantly improves accuracy) First day you got a positive LH test (OPK) this cycle. LH surge typically precedes ovulation by 24–36 hours (range: 22–56h). Enter the date of the first positive — not the peak line.
Age * Used for ASRM-aligned counselling about time-to-pregnancy expectations and when to seek fertility evaluation (≥35: consult after 6 months; <35: after 12 months).
PCOS Status * PCOS causes chronically elevated baseline LH which can produce false-positive OPK readings on many days — not just at ovulation. This significantly affects OPK reliability and ovulation prediction confidence.
How many cycles have you been trying? * ASRM recommends fertility evaluation after 12 months (age <35) or 6 months (age ≥35) of unprotected intercourse. We'll flag when evaluation is advisable.

Wilcox et al. NEJM 1995/2000 · ASRM 2022 · Stanford & Dunson · Cochrane 2023 · LH surge 22–56h range

OVULATION ESTIMATE (ASRM)
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Complete the form to see your fertile window
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Heart Disease Risk (FRS) Framingham 10-year CVD risk · South Asian calibrated

WHAT YOU GET

🌸
6-Day Fertile WindowASRM definition · Wilcox et al. cohorts
⚡
LH Surge Integration22–56h ovulation interval · refined estimate
📊
Day-by-Day ProbabilityVery High · High · Low · Minimal tiers
🔴
PCOS-Aware ScoringDowngrades OPK reliability · flags anovulation
📅
Full Cycle CalendarPhases: menstrual · follicular · ovulation · luteal
⚕️
Clinical Evaluation FlagsASRM referral guidance based on age + duration

WANT MORE?

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EVIDENCE BASE

Wilcox et al. (1995, 2000)NEJM — fertile window, fecundability
ASRM (2022)Optimizing Natural Fertility guidelines
Stanford & Dunson (2007)Day-specific conception probabilities
Cochrane (2023)Timed intercourse systematic review
Stirnemann (2013)Luteal phase duration 7–19 days

RELATED TOOLS

🔬
PCOS Risk CalculatorRotterdam criteria · hormonal profile
 🩺
Diabetes Risk CalculatorFINDRISC + IDRS · insulin resistance
 🩸
Hypertension RiskESH/ESC · DASH · BP risk scoring
 ❤️
Heart Disease Risk (FRS)Framingham · South Asian calibrated

⚕️ This calculator provides evidence-based estimates of ovulation and fertile window timing for conception-support purposes only. It is NOT suitable for contraception or for diagnosing infertility, anovulation, or any reproductive disorder. Ovulation timing is highly variable even in regular cycles — estimates represent probabilities, not guarantees. Women with PCOS, endometriosis, premature ovarian insufficiency, recent hormonal contraceptive use, or known infertility should consult a reproductive endocrinologist or gynaecologist. ASRM recommends fertility evaluation after 12 months of unprotected intercourse (age <35) or 6 months (age ≥35). Seek immediate evaluation for known conditions likely to impair fertility.