Fertility Calculator
Optimize your conception journey with an evidence-based fertility schedule, recommended intercourse timing, and LH testing milestones.
Plan Your Conception Window
Enter your last period date to calculate peak fertility days.
How This Fertility Calculator Works
Conception depends on overlapping the finite lifespans of sperm (up to 5 days in estrogen-rich cervical fluid) and the human oocyte (12–24 hours). By subtracting your luteal phase from your projected next cycle start, we determine the exact 6-day fertile window.
Worked Example
For a woman with an LMP of March 4, 2026, a 28-day cycle, and a 14-day luteal phase:
- Ovulation Date: March 18 (Cycle Day 15)
- Fertile Window: March 13 through March 18
- Peak Conception Days: March 16, 17, 18
- LH Testing Start: March 13 (Cycle Day 10)
Fertility Tracking Checklist for Trying to Conceive
- Cervical Fluid: Look for slippery, clear, stretchy mucus.
- LH Tests: Test urine in the early afternoon (12 PM to 6 PM) for surge detection.
- Prenatal Vitamins: Ensure you are taking at least 400 mcg of folic acid daily.
What This Calculator Cannot Do
- It cannot guarantee pregnancy in any given cycle.
- It cannot assess tubal patency, sperm morphology, or endometrial receptivity.
- It should not be used as contraception.
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)
Frequently Asked Questions
Evidence-based answers to common questions about your cycle and fertility.
How does this fertility calculator determine my fertile window?
The calculator projects your upcoming ovulation day by subtracting your luteal phase (typically 14 days) from your expected next period. Because sperm survive up to 5 days and an egg survives up to 24 hours, your fertile window spans the 5 days prior to ovulation plus ovulation day itself.
How often should we have intercourse during the fertile window?
Having intercourse every 1 to 2 days throughout the 6-day fertile window maximizes the likelihood of viable sperm being present in the fallopian tubes. Daily or every-other-day timing ensures optimal sperm motility and count.
When should I start taking ovulation (LH) tests?
You should begin testing with urinary LH strips approximately 4 to 6 days before your estimated ovulation day (for example, Cycle Day 10 in a 28-day cycle) to ensure you capture the initial surge.
Does having sex after ovulation lead to pregnancy?
The probability of conception drops to less than 1% beyond 24 hours after ovulation, as the unfertilized egg rapidly disintegrates and cervical fluid becomes hostile to sperm penetration.
When should a couple seek clinical fertility evaluation?
According to ACOG guidelines, couples should consult a fertility specialist or OB/GYN after 12 months of timed unprotected intercourse if the female partner is under 35, or after 6 months if aged 35 or older.
Ovulation Calculator
Calculate your estimated ovulation date, 6-day fertile window, and peak conception days. 100% private, client-side calculator with zero tracking.
Conception Calculator
Estimate your probable conception dates and fertile window from your last period, ultrasound, or due date. Pure client-side calculations.
Implantation Calculator
Calculate your estimated implantation window, earliest pregnancy test date, and clinical milestones based on ovulation or conception timing.
Pregnancy Test Date Calculator
Find the earliest possible and most reliable dates to take a home pregnancy test based on ovulation timing or your missed period date.
Medical & Scientific Sources
- American Society for Reproductive Medicine (ASRM)(2022). "Optimizing natural fertility: a committee opinion"
- Wilcox AJ, et al. (NEJM)(1995). "Timing of Sexual Intercourse in Relation to Ovulation"