Ovulation calculator

How ovulation timing works

Ovulation is the day an ovary releases an egg. It usually happens about 14 days before the next period starts, not 14 days after the last one, so in a 28-day cycle it falls around day 15, and in a 32-day cycle around day 19. The egg lives for about a day, but sperm can survive in the body for several days (up to 7, says the NHS). In Wilcox and colleagues’ study, pregnancies came only from sex in a six-day fertile window: the five days before ovulation and ovulation day itself. The best chances are on the two days before ovulation and the day itself.

This tool counts back from your next expected period. It is a calendar estimate: a kind, simple starting point, never a guarantee.

Meena’s first months of trying, in Salem

Meena is 29 and lives in Salem. Her periods come about every 32 days, and her last one began on 1 October 2026. The tool shows a likely ovulation day of Monday 19 October, fertile days of 14–19 Oct 2026, her next period around 2 November, and a pregnancy test from that day if her period doesn’t come.

Her sister Lakshmi, in Kallakurichi, has cycles anywhere from 26 to 35 days. With Irregular, the tool gives a much wider window, 12–28 Oct 2026 for a period that began on 5 October, and suggests LH test strips to narrow it down.

The method

• Regular cycles: ovulation = first day of your last period + cycle length − 14 days (the luteal phase). Fertile days = the 5 days before ovulation and ovulation day. Your next period = last period + cycle length. If you know your own luteal phase from tracking, set it under My cycle details.
• Irregular cycles: the calendar (rhythm) method takes your shortest and longest cycles: first fertile day = shortest − 18, last fertile day = longest − 11, counting the first day of your period as day 1.
• Chance by day: the chart and bars show the relative chance on each day, the best day as 100, from Wilcox, Weinberg and Baird’s study of 221 women in the New England Journal of Medicine (1995), which found about a 10% chance per cycle from sex five days before ovulation rising to about 33% on ovulation day. These are relative guides to timing, not your chance of pregnancy.
• Pregnancy test: most tests work from the first day of a missed period; if you don’t know when it is due, test at least 21 days after unprotected sex (NHS guidance).
• Due date: about 40 weeks from the first day of your last period, adjusted for your cycle length (ovulation day + 266 days).

Signs your body may give

Many people notice some of these around ovulation. None is certain on its own, and it is fine to notice none:

• Clearer, stretchy cervical mucus, like raw egg white, in the days before ovulation.
• A small rise in waking temperature (about 0.2–0.5 °C) after ovulation.
• A mild one-sided twinge in the lower tummy (mittelschmerz).
• Higher sex drive or light spotting for some.
• A positive LH (ovulation) test, 12–36 hours before ovulation.

When to see a doctor

Please see a gynaecologist if your cycles are often shorter than 21 days or longer than 35, vary by more than a week, stop for three months or more, or if you have been trying for a year (six months if you are 35 or older). Polycystic ovary syndrome (PCOS, often called PCOD in India) is common and very manageable once diagnosed.

Common mistakes

• Counting 14 days from the period. Ovulation is about 14 days before the next period, so long cycles ovulate later.
• Using it as birth control. Calendar dates can be off by several days, and the rhythm method is one of the least reliable ways to avoid pregnancy. Talk to a doctor about contraception.
• Starting the cycle on spotting days. Day 1 is the first day of real bleeding.
• Worrying about one odd month. Stress, travel, illness and festivals can shift one cycle; look at the pattern over several months.