Period Calculator
Predict your next periods, ovulation date, and fertile window based on your last period and average cycle length
20 days45 days
1 day10 days
Your Period Predictions
Enter your last period date and cycle length, then click Calculate.
Legend:
Period days
Ovulation day
Fertile window
Frequently Asked Questions
The calculator adds your average cycle length to the first day of your last period to predict your next period. For example, if your last period started on 1 May and your cycle is 28 days, your next period is expected around 29 May. Ovulation is estimated at cycle length − 14 days from the start of each period.
A normal menstrual cycle ranges from 21 to 35 days, with 28 days being the average. Cycle lengths can vary month to month by a few days. Consistently very short (<21 days) or very long (>35 days) cycles should be discussed with a healthcare provider.
The fertile window is typically the 5 days before ovulation plus the day of ovulation itself. Since sperm can survive up to 5 days in the female reproductive tract, intercourse in this window can lead to pregnancy. Ovulation usually occurs about 14 days before the next expected period.
Predictions are based on your stated average cycle length and are a good starting point. However, cycles can be influenced by stress, illness, travel, hormonal changes, and other factors. For family planning or medical decisions, always consult a healthcare professional and consider tracking multiple cycles to find your personal average.
If your cycles vary significantly, try using the average of your last 3–6 cycles as your cycle length input. Irregular periods can be caused by PCOS, thyroid conditions, stress, or significant weight changes. A doctor can help identify the underlying cause and provide personalised guidance.
About This Period Calculator
This free Period Calculator predicts your upcoming menstrual periods, ovulation dates, and fertile windows for up to 12 months ahead. Based on your last period date and average cycle length, it helps you plan ahead, understand your cycle, and identify your most fertile days — all without any sign-up or personal data stored.
