Ovulation calculator: your fertile window and next period

Ovulation usually happens about 14 days before your next period starts, not always on day 14 of the cycle. With a 28-day cycle that is around day 14, with a 35-day cycle around day 21, and with a 24-day cycle around day 10. Count the first day of bleeding as day 1.

The fertile window is about 6 days: the 5 days before ovulation and the day of ovulation. Sperm can survive up to 5 days in the womb, while the egg survives only about 12 to 24 hours after it is released. The two days just before ovulation and ovulation day have the highest chance of pregnancy.

Regular intercourse every 2 to 3 days through the month is recommended by NICE and gives a good chance without having to time it exactly. In the fertile window, every 1 to 2 days is best. Timing intercourse only to a calculator can add stress and miss ovulation, because the estimate can be off.

It is a calendar estimate and is most useful for women whose cycles are within a few days of the same length each month. Ovulation can move a week or more with stress, illness, travel, weight change, thyroid problems, PCOS, breastfeeding or coming off hormonal contraception. Ovulation test strips (LH tests) detect the hormone surge and are more reliable.

Some women notice clear, stretchy, egg-white-like vaginal mucus, a mild one-sided lower-belly ache for a few hours, slight spotting, breast tenderness or a higher sex drive. A body temperature taken on waking rises slightly (about 0.2 to 0.5 °C) after ovulation. None of these are required, and many women notice nothing.

It is much less likely, but not impossible, because ovulation can shift in a given month. Never rely on this calculator to avoid pregnancy; use a method recommended by your doctor.

Not reliably. In PCOS ovulation may be rare or unpredictable, so a calendar cannot tell you when it will happen. Use LH strips and see a doctor. The first-line treatment for PCOS with excess weight is lifestyle change: even a 5 percent weight loss can restart ovulation in many women. See our PCOS diet plan.

No food or supplement can force ovulation. What helps is a stable weight in a healthy range (both very high and very low body weight can stop ovulation), a balanced diet with enough protein, iron and fibre, regular meals, not smoking, limiting caffeine to about 200 mg a day (roughly 2 cups of chai or one coffee), and managing PCOS or thyroid disease if you have it.

Yes. Guidelines advise 400 micrograms (0.4 mg) of folic acid a day starting at least a month before trying to conceive and until week 12, to lower the risk of neural tube defects. Women with diabetes, obesity, epilepsy, a previous affected pregnancy or those on certain medicines need a higher dose prescribed by a doctor.

See a doctor after 12 months of regular intercourse without pregnancy if you are under 35, after 6 months if you are 35 or older, and earlier if your periods are very irregular or absent, you have known PCOS, endometriosis, thyroid disease or past pelvic infection. Both partners should be checked.