Enter the first day of your last period and your usual cycle length to estimate your fertile window for the next 3 cycles. It's free, and nothing you enter is saved or sent anywhere.
How This Ovulation Calculator Works
The NHS says ovulation usually happens 10 to 16 days before your next period, so this calculator uses 14 days as its best estimate and shows the full range. Your fertile window is about 6 days: the 5 days before ovulation and the day of ovulation itself, because sperm can survive for several days. Your chances are highest in the last 2 to 3 days up to ovulation.
Limits of Any Ovulation Calculator
A calculator only predicts. Cycles vary from month to month, especially if they're irregular, after stopping hormonal contraception, after having a baby, with PCOS, or in perimenopause. To confirm ovulation, look for clear, stretchy cervical mucus, or use urine ovulation tests. Our guide to how to know when you're ovulating explains each sign. Never use a calculator as contraception.
When to See a Doctor
The NHS suggests seeing a GP if you haven't got pregnant after a year of trying, or sooner if you're 36 or over or know of a possible fertility problem. Mention it too if your cycles are often shorter than 21 days or longer than 35.
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Perimenopause symptom & cycle tracker
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About the author: Jessica Bordo writes Daily Health Cycle out of personal interest in women's health, not as a clinician. Each guide summarizes what sources such as the NHS, NICE and published studies say, and links to them so you can check the claims yourself. Use these guides to prepare questions for your own clinician, not to replace their advice.
This tool gives estimates for general education and isn't medical advice or a method of contraception. See our full disclaimer.