Menstrual Cycle Calculator
Predict your upcoming menstrual cycles.
Tip: A normal cycle lasts 21–35 days. If it varies a lot, consult a doctor.
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About this digital tool
The menstrual cycle calculator predicts the dates of the next three cycles from the first day of your last period, your cycle length and the duration of your period. For each cycle you get the start and end dates, and the cycle day you are on today.
The calculation is simple: start of the next cycle = last date + cycle length, repeated for the following cycles. Cycle length is counted from the first day of one period to the first day of the next; the average is 28 days, but 21-35 days is considered normal. The prediction is an estimate, because stress, illness or hormonal changes can shift the cycle. If your cycle changes a lot or you have severe pain, consult a gynaecologist.
How to use
- Enter the date of your last period.
- Set your average cycle length.
- See the prediction for the next few cycles.
Frequently asked questions
How many days does a normal cycle last?
21–35 days is considered normal. The average is 28 days, but many women have slightly shorter or longer cycles.
How is menstrual cycle length calculated?
Count the days from the first day of one period to the day before the next one starts. For accuracy, measure several cycles and take the average.
Is it normal for a period to be a few days late?
Yes, small variations from month to month are common. If periods are missing for a long time, you suspect pregnancy or changes keep recurring, consult a doctor.
What are the phases of the menstrual cycle?
The cycle has four phases: menstrual, follicular, ovulatory and luteal. Ovulation occurs roughly in the middle of a 28-day cycle.