Ovulation Calculator

If you are trying for a baby, timing matters: an egg lives for about a day, while sperm can survive for up to five. This calculator estimates the six days each cycle when sex is most likely to lead to pregnancy, picks out the two or three best ones, and shows them for your next three or six cycles along with the day you are likely to ovulate, when your next period is due and the first day a home test is reliable.

Most calculators assume ovulation on day 14. This one works backwards from your next period using your luteal phase, the stretch between ovulation and your period, which is usually about 14 days. So a 32-day cycle gives a later fertile window than a 28-day one, and if ovulation tests have shown you a shorter or longer luteal phase you can set it. Results appear as cycle-by-cycle cards and as a month calendar where every day is marked with a shape as well as a colour.

It runs entirely in your browser. Your dates stay on your device and nothing is saved. It is a planning aid built on averages, not medical advice, and it is not a form of contraception.

1. Enter the first day of your last period.
2. Choose your average cycle length and how long your period usually lasts.
3. Leave the luteal phase at 14 days unless you know yours, and choose 3 or 6 cycles to show.
4. Read your next fertile window, estimated ovulation and today’s place in your cycle.
5. Use the calendar arrows or “This month” to browse, then press “Copy dates” to save the list.

• Fertile window (five days before ovulation plus ovulation day) and the three most fertile days.
• Ovulation worked out from your cycle length and luteal phase, not a fixed day 14.
• Cycle lengths from 21 to 45 days, period length from 1 to 10 days and luteal phase from 9 to 17 days.
• The next 3 or 6 cycles, each with period, fertile days, ovulation, next period and test date.
• A two-month calendar with a legend; days are marked by fill, dashed outline and a star, not colour alone.
• Tells you where today falls in your cycle, and notices when a period looks overdue.
• The due date you would have if you conceived in each cycle.
• Copy all the dates as plain text, shown in your own language and date order.

• Use an average of your last few cycles, counted from the first day of one period to the day before the next.
• Sex every one to two days through the fertile window works better than trying to hit one exact day.
• Ovulation predictor kits and noting your temperature or cervical mucus show what your body is doing this cycle. Use them alongside these dates.
• If your cycles vary by more than about a week, treat the dates as rough and lean on ovulation tests instead.
• Start from your most recent period each month so the dates stay accurate.