Fertility Window Estimator

Estimate your best days to conceive

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Medical Disclaimer: This tool is for educational and informational purposes only. It does not provide medical advice, diagnosis, or treatment. Results are estimates only. Always consult a qualified healthcare professional for medical decisions. In an emergency, call 995 (Singapore) immediately.

Understanding Your Menstrual Cycle

Menstrual Phase Days 1–5

Your uterine lining sheds. This is the start of your cycle. Light exercise is fine. Some women track basal body temperature (BBT) starting from day 1.

Follicular Phase Days 1–13

Your body prepares for ovulation. Follicles in your ovaries grow under the influence of FSH. Estrogen rises, your energy increases, and cervical mucus begins to appear.

Fertile Window Days 8–15

The 5 days before ovulation plus the day of ovulation itself. Sperm can survive up to 5 days in the female reproductive tract, so sex during this window maximises conception chances. Cervical mucus becomes clear and stretchy (egg-white consistency).

Ovulation Day 14 (avg)

A surge in LH (luteinising hormone) triggers the release of a mature egg from the ovary. The egg survives only 12–24 hours. If sperm is present, fertilisation can occur. Signs: mild one-sided pelvic pain (Mittelschmerz), increased libido, stretchy cervical mucus.

Luteal Phase Days 15–28

The empty follicle becomes the corpus luteum and secretes progesterone, thickening the uterine lining for implantation. If fertilisation does not occur, progesterone drops and your period begins. BBT rises ~0.2°C after ovulation.

Signs of Ovulation to Watch For

Sign	What to Look For	Reliability
Cervical Mucus	Clear, stretchy, egg-white texture (peak fertility)	High
BBT rise	Temperature rises ~0.2°C after ovulation (confirms it happened)	High (retrospective)
LH Surge (OPK)	Ovulation predictor kit turns positive 12–36h before ovulation	Very High
Mild Pelvic Pain	One-sided cramping (Mittelschmerz) at ovulation time	Moderate
Increased Libido	Natural rise in desire around fertile window	Low – varies widely
Light Spotting	Faint pink/brown spotting at ovulation (not all women)	Low – uncommon

Tracking multiple signs together (BBT + OPK + mucus) gives the most accurate picture of your fertility window. For more, visit the TTC Guide →

Fertility by Age: What the Data Shows

Under 25 ~25% per cycle

25–29 ~22% per cycle

30–34 ~18% per cycle

35–37 ~13% per cycle

38–40 ~8% per cycle

41–43 ~4% per cycle

44+ ~2% per cycle

Chance of conception per natural cycle. Source: ACOG / Fertility research reviews. Fertility declines with age - If you have been trying for 12 months without success (6 months if over 35), speak to your doctor about a fertility evaluation.