Period Calculator

Estimate your next period date and approximate fertile window. This is only an estimate and not medical advice.

First day of your last period Average cycle length (days)

Disclaimer: This tool provides approximate dates only and should not be used as a method of birth control or for medical decisions. Please consult a doctor for personalised advice.

What is a Menstrual Cycle?

The menstrual cycle is a monthly process in which the body prepares for pregnancy. It is counted from the first day of one period to the first day of the next. The average menstrual cycle length is 28 days, but it can range from 21 to 35 days in adults and is considered normal. Each cycle involves hormonal changes that trigger ovulation (release of an egg) and, if the egg is not fertilised, menstruation (shedding of the uterine lining).

How to Use This Period Calculator

1. Select the first day of your last menstrual period from the date picker.

2. Enter your average cycle length in days (leave as 28 if unsure).

3. Click "Calculate" to see your estimated next period date, ovulation day and fertile window.

Understanding the Ovulation Window

Ovulation typically occurs about 14 days before the start of the next period. The fertile window spans approximately 5 days before ovulation and 1 day after. During this window, the chances of conception are highest. This calculator estimates the ovulation day and fertile window based on your cycle length, but individual cycles can vary.

Frequently Asked Questions

How accurate is this period calculator?

This calculator provides an estimate based on average cycle patterns. It works best for women with regular cycles. Factors like stress, illness, weight changes and hormonal conditions can affect cycle length and ovulation timing. It should not be used as a method of contraception.

What if my cycle is irregular?

If your cycle varies significantly each month (shorter than 21 days or longer than 35 days), this calculator may not provide accurate predictions. Track your periods for several months to find your average cycle length, or consult a gynaecologist for personalised advice.

Should I rely on this tool for medical decisions?

No. This tool is for informational and planning purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Always consult a qualified healthcare provider for any health concerns or family planning decisions.