Period Calculator
Predict your next period, ovulation day and fertile window from your last period and cycle length
基础信息
💡 月经周期为两次月经第一天的间隔天数，正常范围 21-45 天。排卵通常发生在下次月经前 14 天
请输入上次月经日期后点击「开始计算」
About this tool
The period calculator predicts your menstrual cycle and fertile window:
- Next period: estimate the start date from your last period and cycle length
- Ovulation: estimate the ovulation day, about 14 days before the next period
- Fertile window: the five days before ovulation through the four days after
- Safe days: the lower-probability days outside that window
- Several cycles: project period dates for the next three months
When to use it
- Trying to conceive: time intercourse around ovulation
- Contraception: understand safe days as a supplement, not a guarantee
- Health tracking: record and follow the rhythm of your cycle
- Planning: schedule trips around your period
How it is calculated
- Ovulation: usually about 14 days before the next period begins
- Fertile window: sperm survive three to five days and an egg about one day, so the five days before ovulation and four days after form the window
- Cycle length: a normal cycle runs 21 to 35 days, averaging 28
- Reference only: real ovulation depends on many factors; use these dates as a guide, not a medical conclusion