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Ovulation calculator

Estimate the day you are likely to ovulate and the days when you are most likely to conceive. Enter the first day of your last period and your usual cycle length.

Important: This calculator estimates your fertile window from the average length of your cycles. It is most useful if your cycles are fairly regular, and it cannot tell you exactly when you ovulate. It is not a method of contraception. If you are trying to avoid pregnancy, speak to a doctor, nurse or pharmacist about reliable options.

Your dates are processed in this page and are not sent to our server or saved by this tool.

How the calculator works

Ovulation usually happens about 12 to 14 days before your next period starts, not on a fixed day of the cycle. We take your cycle length, subtract your luteal phase (14 days unless you change it), and count forward from the first day of your last period.

Your fertile window is the six days that end on the day after ovulation. Sperm can survive for up to five days inside the body, while an egg survives for only around 12 to 24 hours after it is released. That is why having sex in the days before ovulation matters as much as on the day itself.

Signs that you may be ovulating

Cervical mucus: clear, slippery and stretchy, a little like raw egg white, in the days around ovulation.
A mild twinge or ache on one side of your lower abdomen, which some people notice for a few hours.
A rise in basal body temperature of a small amount (about 0.2 to 0.5 °C) after ovulation. It confirms that ovulation has already happened rather than predicting it.
A positive ovulation test: these kits detect the hormone surge that comes about one to two days before the egg is released.

If your cycles are irregular

A calculator works best when your cycles are within a few days of the same length each month. If they vary a lot, the dates above can be off by a week or more. Tracking cervical mucus or using ovulation tests can give you a better idea. If your periods are very irregular or have stopped, ask your doctor, because it may be a sign that you are not ovulating regularly.

How long to try before asking for help

Most couples conceive within a year of regular, unprotected sex. See your doctor if you have been trying for a year without success, or after about six months if you are 35 or older. Do not wait if you already know of a problem, such as very irregular periods, pelvic infections or endometriosis. Read more in our guides to ovulation and the fertile window and fertility myths and facts.

Getting ready for pregnancy

Start taking folic acid before you conceive. Our guide to folic acid and prenatal vitamins explains the usual dose and why it helps.
Work through the pre-pregnancy checklist.
Fertility is shared between partners. See fertility and your partner.
If you think you may be pregnant, the pregnancy test calculator helps you pick the best day to test.

Prefer official guidance? Read the NHS advice on trying for a baby.