Period Cycle Calculator

Estimate your next period start date, ovulation date, and fertile window from your latest period start.

Latest period start date

Average cycle length

In days, usually between 20 and 45

Average period length

In days, usually between 1 and 10

This calculator provides estimates for reference only. Actual ovulation, fertile window, and period dates can vary by individual health conditions and lifestyle factors.

Period cycle calculator

Estimates next period, ovulation, and fertile window.

From last period start and average cycle length, it estimates next period start, ovulation date, and fertile days.

Average cycle length is often around 28 days; individual variation is typically 20–45 days.E.g. 28-day cycle, 5-day period → next period, ovulation, and fertile window are estimated.

Ovulation: Ovulation is when a mature egg is released from the ovary and can be fertilised. It is often assumed to occur about 14 days before the next period.
Fertile window: The fertile window is the days when conception is most likely, usually including the days before and the day of ovulation, based on sperm and egg survival.