Ovulation and fertile window calculator
Ovulation date and fertile window from LMP and average cycle length.
About this calculator
The ovulation and fertile window calculator estimates the most favorable days to conceive. Based on Wilcox et al. (NEJM, 1995) data from 221 healthy women with regular cycles. The fertile window is 6 days: 5 days before ovulation and the day of ovulation (sperm live 3-5 days in the lower genital tract, the oocyte 12-24 hours after ovulation). Calculation. Ovulation occurs 14 days before the next menses (midcycle on day 14 of a 28-day cycle). For irregular or different-length cycles – ovulation is on day N - 14, where N is cycle length. Fertile window – days N-19 through N-14. Clinical use. Conception support in a normal couple. Targeting the fertile window without overly frequent intercourse raises pregnancy rates per cycle from 20% to 30%. Does not provide contraception – the calendar method has a 24% annual failure rate (WHO 2018 Pearl index). Modern ovulation tracking alternatives – urinary LH tests (95% accuracy with proper use), ultrasound follicle tracking, basal body temperature. When used. Regular 21-35-day cycle. Absence of PCOS, hypothalamic amenorrhea, hyperprolactinemia. After stopping oral contraceptives cycles usually restore within 1-3 months; until then calculation is inaccurate. In women over 35 the fertile window may be shorter due to irregular ovulation – reproductive specialist consultation is warranted after 6 months of attempts; under 35 – after 12 months. Limitations. Not valid in irregular cycles, anovulatory cycles, PCOS, endometriosis, hypothyroidism, hyperprolactinemia, severe stress, high-intensity sports, eating disorders. Does not predict pregnancy – only raises chances in absence of medical infertility causes. Does not replace reproductive specialist evaluation when conception fails.
Source
Formula version: wilcox-1995-asrm-2024-v1
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