Menstrual Cycle Calculator

Knowing when your next period is due and when your fertile window falls helps with family planning, health tracking, and managing day-to-day life. This calculator uses your last period date and average cycle length to project your next period, estimate ovulation, and identify your likely fertile days. How to use it: Enter the date your last period started and your average cycle length in days. If you are not sure of your exact cycle length, 28 days is the standard average — but cycle lengths vary considerably between individuals, commonly ranging from 21 to 35 days. If you track your periods regularly, use your own average from the last 3 to 6 months for more accurate predictions. What the calculator shows: Next period date — estimated by adding your cycle length to your last period start date. Ovulation date — estimated as cycle length minus 14 days from the start of the next period. For a 28-day cycle, ovulation typically falls around day 14. For a 32-day cycle, around day 18. Fertile window — the 5 days before ovulation plus ovulation day itself, when conception is most likely. Period end date — estimated based on your average period duration (default 5 days, adjustable). Future cycle projections: The calculator shows the next 3 to 6 cycle projections, so you can plan ahead for events, travel, or medical appointments. Important considerations: Cycle predictions are estimates based on the assumption of a regular cycle. Stress, illness, weight changes, hormonal conditions (PCOS, thyroid issues), and contraception use all affect cycle timing. A difference of a few days between the prediction and your actual period is normal and does not indicate a problem. This tool is for tracking and planning purposes only. It is not a medical diagnostic tool. For fertility planning or concerns about irregular cycles, consult a healthcare provider.