Frequently asked questions
How accurate is ovulation prediction from cycle length alone?
It is a reasonable estimate for women with regular cycles. The 'ovulation = cycle length minus 14 days' rule assumes a consistent luteal phase, which holds for most women within 1 to 2 days. However, stress, illness, and hormonal fluctuations can shift ovulation. For greater precision, use ovulation predictor kits (OPKs) or basal body temperature tracking.
What is the fertile window and why is it 6 days?
Sperm can survive in the reproductive tract for up to 5 days, and the egg is viable for about 12 to 24 hours after ovulation. This creates a roughly 6-day window (5 days before ovulation plus ovulation day itself) during which intercourse can result in pregnancy.
Can I get pregnant outside the fertile window?
It is highly unlikely but not impossible. In rare cases ovulation can occur earlier or later than predicted, especially with irregular cycles. The calculated window is the most probable time, not a guarantee. If you are trying to avoid pregnancy, use reliable contraception throughout the cycle.
Does cycle length change which day I ovulate?
Yes. The luteal phase (after ovulation) is relatively fixed at about 14 days. The follicular phase (before ovulation) is what varies. A 35-day cycle means ovulation around day 21, while a 24-day cycle means ovulation around day 10. This calculator adjusts for your specific cycle length.
What are signs that ovulation is occurring?
Common signs include a slight rise in basal body temperature (0.2 to 0.5 degrees Celsius), changes in cervical mucus (becoming clear and stretchy, like egg whites), mild pelvic pain on one side (mittelschmerz), increased libido, and a positive ovulation predictor kit (detecting the LH surge).
Should I use this calculator for contraception?
No. Calendar-based fertility awareness methods have typical-use failure rates of 12 to 24% per year. This calculator provides estimates based on averages and cannot account for cycle irregularities. For reliable contraception, consult a healthcare provider about proven methods.