Predict your next 3 periods, fertile windows, and ovulation dates based on your last period date and cycle length.
This calculator provides estimates based on average cycle patterns. Individual cycles can vary significantly. This tool is for informational purposes only and does not constitute medical advice. Consult your GP or visit the NHS website for concerns about your menstrual cycle.
Tracking your period cycle helps you understand your body, plan ahead, and identify any irregularities that might need medical attention. A typical menstrual cycle lasts between 21 and 35 days, with 28 days being the average according to the NHS. Your cycle begins on the first day of your period and ends the day before your next period starts. During each cycle, your body goes through four distinct phases: menstruation, the follicular phase, ovulation, and the luteal phase. By entering your last period date and average cycle length, this calculator predicts your next three periods, estimates your ovulation date, and identifies your fertile window. While these predictions are based on averages and may not account for individual variations, they provide a useful guide for cycle awareness.
To predict your next periods and fertile window: 1. Enter the first day of your last period using the date picker. This should be the first day of bleeding, not spotting. 2. Set your average cycle length. If you are unsure, 28 days is a good starting point. Track your cycle over 3-6 months for a more accurate figure. The NHS considers cycles between 21 and 35 days to be normal. 3. Set your period length, which is how many days your period typically lasts. Most periods last between 3 and 7 days. 4. Review your results, which show your next three predicted period dates, estimated ovulation date, fertile window, and current cycle phase. The chart shows a visual breakdown of your cycle phases.
The period cycle calculator uses established medical principles to predict cycle events: Your next period date is calculated by adding your cycle length to your last period date. The second and third periods add 2x and 3x the cycle length respectively. Ovulation is estimated at 14 days before your next period. This is based on the medical understanding that the luteal phase (the time between ovulation and your next period) is consistently around 14 days in most women, regardless of total cycle length. For a 28-day cycle, ovulation occurs around day 14; for a 32-day cycle, around day 18. The fertile window spans 6 days: from 5 days before ovulation to 1 day after. This accounts for the fact that sperm can survive in the reproductive tract for up to 5 days, and the egg remains viable for approximately 24 hours after release. Your current cycle phase is determined by comparing today's date to the cycle timeline. The calculator identifies whether you are in menstruation, the follicular phase, the ovulation window, or the luteal phase.
Inputs: Last period: 1 March 2026, Cycle length: 28 days, Period length: 5 days
Inputs: Last period: 1 March 2026, Cycle length: 32 days, Period length: 5 days
This calculator provides estimates based on average cycle patterns. The NHS advises that cycles can vary by a few days each month and this is perfectly normal. Factors such as stress, illness, weight changes, and exercise can all affect cycle regularity. If your periods are consistently irregular, very heavy, or painful, consult your GP. This calculator should not be used as a contraception method.