In a typical cycle, ovulation happens about 14 days before the next period starts. So for a 28-day cycle, ovulation lands on day 14; for a 32-day cycle, around day 18. The tool adds the 5 pre-ovulation days (sperm survival) and 1 post-ovulation day (egg survival) to build the full fertile window. If you track temperature, cervical mucus or use OPK strips, you can fine-tune these estimates cycle by cycle.
典型周期中，排卵发生在下次月经前约 14 天。因此 28 天周期在第 14 天排卵；32 天周期约在第 18 天。本工具加上排卵前 5 天（精子存活期）与排卵后 1 天（卵子存活期），构成完整受孕窗口。如果你记录基础体温、宫颈黏液或使用排卵试纸，可逐周期微调这些估算。
