Period Calculator

Predict your next period, fertile window, and ovulation date based on cycle history.

Result

Fill in the fields above, then press Calculate.

A period calculator predicts your next menstrual period and fertile window based on your cycle history.

Enter the first day of your last period, your average cycle length, and how many days your period typically lasts. The calculator predicts your next 6 periods, ovulation dates, and fertile windows, and shows your current cycle phase.

Examples

28-day cycle starting January 1

Next period: January 29. Ovulation: January 15 (day 14). Fertile window: January 10-16.

Frequently Asked Questions

How accurate are period predictions?
Predictions are based on your average cycle length and assume regularity. Factors like stress, illness, travel, and hormonal changes can cause cycles to vary. Track several months for better predictions.
What are the phases of the menstrual cycle?
The four phases are: Menstrual (days 1-5, bleeding), Follicular (days 1-13, egg development), Ovulation (day 14, egg release), and Luteal (days 15-28, uterine lining thickens). Actual timing varies by individual.
Related Calculators
Ovulation Calculator
Due Date Calculator
Conception Calculator
Pregnancy Calculator

Quick Tips

  • •Log your period start dates consistently for at least 3 cycles to improve prediction accuracy.
  • •Note any unusual symptoms or changes in flow, as these can indicate cycle irregularities.
  • •Always confirm results with your healthcare provider if you have concerns about your cycle.