Period Calculator
About the Period Calculator
This period calculator predicts your next 6 menstrual cycles, including period dates, ovulation day, and fertile window. Understanding your cycle patterns helps with family planning and tracking reproductive health.
The Formula
Next period start = LMP + (cycle length × n). Period end = period start + period length − 1. Ovulation day = period start + cycle length − 14 (assuming a 14-day luteal phase). Fertile window = ovulation day − 5 through ovulation day.
Frequently Asked Questions
How accurate are period predictions?
For regular cycles (similar length each month), predictions are fairly reliable. Irregular cycles may vary by several days. Tracking for 3–6 months improves prediction accuracy by identifying your average cycle length.
What factors can affect cycle length?
Stress, illness, travel, significant weight changes, exercise intensity, hormonal contraceptives, and conditions like PCOS or thyroid disorders can all affect cycle length. A variation of 1–2 days between cycles is normal.