The fertile window is the time during which conception is possible. Since sperm can live in the uterus or fallopian tubes for up to 5 days and an egg can live for up to 24 hours after ovulation, the fertile window is typically 5-7 days long.
Ovulation day and fertile window are based on your cycle length, age, and BMI. These factors are combined with population-level reproductive health research from the NIH to give you a personalized prediction. For most cycles, ovulation occurs about 14 days before the next period. However, individual factors like age and BMI can shift this timing, which we account for in your calculation.
Your fertile window lasts 6 days, starting 5 days before your ovulation day and ending 1 day after. Keep in mind that while this calculator offers personalized estimates, variability in cycles means your actual ovulation day may differ slightly. For the most accurate results, consider pairing these predictions with other fertility tracking methods, like LH tests or basal body temperature tracking.
During ovulation, basal body temperature rises by about 0.5 - 1°F (0.3 - 0.6°C). There are also cervical mucus changes that are observable in discharge—cervical mucus becomes thinner and slicker in order to aid in sperm mobilization. Ovulation predictor kits can also detect the spike in luteinizing hormone (LH) in urine, which occurs within 24 hours prior to ovulation. Spotting and cramping may also occur before, during, and after ovulation.
If you experience irregular cycles, the calculator's predictions may be less accurate. Variability in cycle length can make it difficult to pinpoint ovulation and the fertile window. Additionally, conditions such as polycystic ovary syndrome (PCOS), endometriosis, thyroid disorders, or other reproductive health issues may cause anovulation (cycles where ovulation does not occur), which this tool cannot detect.
This tool is not a diagnostic instrument and is not a substitute for medical advice. If you have concerns about your menstrual health or fertility, or if you suspect you may have a condition affecting ovulation, we recommend consulting with a healthcare provider for personalized guidance and evaluation.
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