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Track your fertile window and estimate your ovulation day with ease. Get clear dates and a cycle calendar based on your personal cycle details.
Better cycle
Awareness
for a healthier
you
Fill in the details below to see your estimated ovulation day and fertile window.
Enter your details and press Calculate to see your estimated fertile dates here.
It is a projection from your average cycle, not a measurement. On a regular cycle the estimate usually lands within a couple of days, but ovulation genuinely moves around, and irregular cycles can be out by much more.
Treat every date as a rough guide. Irregular ovulation is common and often benign, but if your cycles are very irregular, or you have irregular bleeding alongside symptoms that worry you, a clinician should take a look rather than a calculator.
Yes, it helps you understand your cycle and roughly when you are fertile. It is not an assessment of your fertility, and calendar timing cannot guarantee conception. If you have been trying for 12 months under 35, or six months over 35, speak to a clinician.
No. Calendar methods are among the least reliable forms of contraception precisely because ovulation shifts unpredictably. If avoiding pregnancy matters, talk to a clinician about a method that does not depend on timing.
Because the luteal phase varies between people and between cycles. If your estimate feels consistently wrong, the cycle length or last-period date you entered is probably not accurate — and a different number fixes the whole forecast.
No. The calculation runs in your browser. Nothing is sent to a server, written to a database or attached to an account, and the inputs clear when you leave or refresh the page.
Understand your cycle, track important dates, and take charge of your reproductive health.
Explore Health HubThe rule is short enough to work out on paper with your own dates.
Notice the window is wider than the ovulation day itself. That is deliberate: it reflects how long sperm and egg actually survive, not just the moment of release.
Understanding the estimate makes it far easier to read correctly.
A cycle begins when a follicle in one ovary is recruited and grows. In the days before release, rising estrogen makes cervical mucus thin and stretchy, which helps sperm travel. A surge of luteinising hormone — the hormone ovulation predictor kits detect — triggers the release of a mature egg.
If sperm are present, fertilisation usually happens in the fallopian tube within a day of release. If pregnancy does not occur, the corpus luteum breaks down, progesterone falls, and the uterine lining is shed as your next period. Ovulation is the pivot the rest of the cycle turns around, which is why every other date here is measured from it.
If your cycles are irregular, treat every date on this page as a rough guide. If they are regular, the estimate is usually close — but still an estimate.
If you need better than an estimate, these are the options, roughly in order of precision.
Combining two or more signals — cervical mucus alongside basal body temperature, for example — is more dependable than any single one, because each captures a different part of the same process.
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