Ovulation and Period Calculator
Estimate your fertile window, ovulation date and next period using the first day of your last period and your average cycle length.
Cycle dates are estimates for people with reasonably regular cycles. Do not use this calculator as contraception or to confirm pregnancy.
Estimate your cycle dates
Use your average cycle length across recent cycles if you know it.
Your estimate
How the Calculator Estimates Your Dates
A menstrual cycle is measured from the first day of one period to the day before the next period begins. This tool estimates ovulation by counting back 14 days from your next expected period.
The fertile window is shown as the five days before estimated ovulation plus ovulation day. Sperm can survive for several days, while an egg is usually available for fertilisation for a much shorter time.
Why the Estimate Can Change
Ovulation does not always happen on the same cycle day. Stress, illness, travel, weight changes, breastfeeding, perimenopause and some medicines can affect timing. Hormonal contraception can change or prevent ovulation, so these predictions may not apply.
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Frequently Asked Questions (FAQs)
The estimate counts back 14 days from the start of the next expected period. The time from ovulation to the next period can vary, so the result is only a guide.
The estimated fertile window covers the five days before ovulation and the estimated ovulation day. Pregnancy is possible outside predicted dates because cycles vary.
No. An estimated fertile window is not a reliable contraceptive method. Speak with a medical practitioner about contraception suitable for you.
Predictions are less reliable if cycle length changes substantially from month to month. Consider speaking with a GP if periods are irregular, absent, unusually heavy, painful or have changed from your usual pattern.
This tool provides general information only and does not replace medical, legal or workplace advice. If symptoms are severe or life-threatening, call 000.
