What is the fertile window?

The fertile window is the 6-day period during your menstrual cycle when pregnancy is possible. This includes the 5 days leading up to ovulation plus ovulation day itself. Having intercourse during this time gives sperm the opportunity to be present when the egg is released.

Why 6 days?

While an egg only survives 12-24 hours after ovulation, sperm can live in the female reproductive tract for up to 5 days. This means that intercourse in the days before ovulation can still result in pregnancy when ovulation occurs.

Best days for conception

Not all days in the fertile window have equal pregnancy probability. Research shows the highest chances of conception occur on these days:

Days further from ovulation have lower but still meaningful pregnancy rates (5-10% for 3-5 days before ovulation).

How to determine your cycle length

Track your cycle for 2-3 months to determine your average cycle length:

1. Mark the first day of your period as Day 1
2. Count the days until the day before your next period starts
3. This total is your cycle length for that month
4. Calculate the average of 2-3 cycles for the most accurate prediction

Signs of ovulation

Your body gives several clues that ovulation is approaching or occurring:

Tools for tracking

• Ovulation predictor kits (OPKs): Detect the LH surge that occurs 24-36 hours before ovulation. More accurate than calendar methods for pinpointing ovulation.
• Fertility tracking apps: Help you log periods, symptoms, and predict fertile days based on your data
• Basal body temperature (BBT) tracking: Requires daily temperature measurement before getting out of bed. Shows ovulation has occurred (not predictive, but confirms timing)
• Fertility monitors: Advanced devices that track hormones in urine or saliva

When to see a fertility specialist

Consider consulting a healthcare provider if:

• • You're under 35 and haven't conceived after 12 months of trying
• • You're 35 or older and haven't conceived after 6 months of trying
• • You have irregular or absent menstrual cycles
• • You have a history of pelvic inflammatory disease, endometriosis, or PCOS
• • Your partner has known fertility issues

Who this calculator works best for:

• ✅ Women with regular, predictable menstrual cycles (variations of only 1-2 days)
• ✅ Women who know their average cycle length
• ✅ Women not on hormonal birth control
• ✅ Women in their reproductive years (not perimenopausal)

Limitations and factors affecting accuracy:

• Irregular cycles: If your cycle length varies by more than 7-9 days month to month, calendar-based predictions are less reliable. Consider using ovulation tests or tracking additional signs.
• Stress and illness: Physical or emotional stress, illness, travel, and significant lifestyle changes can delay ovulation in a given cycle.
• PCOS (Polycystic Ovary Syndrome): Can cause irregular ovulation or anovulation (no ovulation), making calendar predictions unreliable.
• Recent birth control use: It may take a few months for regular ovulation patterns to resume after stopping hormonal contraception.
• Breastfeeding: Can suppress or delay ovulation, making cycles unpredictable
• Perimenopause: Cycle irregularity increases as women approach menopause
• Thyroid disorders: Can affect cycle regularity and ovulation

More accurate methods:

For more precise ovulation detection, especially if you have irregular cycles, consider:

• Ovulation predictor kits (OPKs): Test urine for LH surge before ovulation (80-95% accurate when used correctly)
• Fertility monitors: Track multiple hormones for more comprehensive fertility tracking
• Ultrasound monitoring: Healthcare provider tracks follicle development via ultrasound
• Blood tests: Measure progesterone levels to confirm ovulation occurred