Ovulation Calculator
Today (Sun, Oct 18) is cycle day 11 — you are in your fertile window, with about a 16% chance of conceiving from sex today. It runs through Thu, Oct 22.
Your next three months
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In the landmark study that tracked 625 cycles, every pregnancy came from sex in the six days ending on ovulation day — none from the day after. Because sperm can survive up to five days and an egg only about a day, the best time is the two or three days leading up to ovulation, not after a positive sign that it has already happened.
With a 28-day cycle that last started October 8, 2026, your current fertile window is Oct 17 – 22, with ovulation most likely around Thu, Oct 22. If you conceive this cycle, a pregnancy test is most reliable from Thu, Nov 5, and your due date would be about July 15, 2027.
- Have sex every day or every other day from Sun, Oct 18 through Thu, Oct 22 — sperm can live up to five days, so the days before ovulation matter most.
- Confirm with ovulation test strips starting Sun, Oct 18 — a positive LH test usually means ovulation within the next 12 to 36 hours.
- Wait until Thu, Nov 5, the day your period is due, before taking a home pregnancy test — testing earlier often gives a false negative.
Key Answers About Your Ovulation and Fertile Days
Each answer is recalculated from the dates you entered above.
Most likely around Thu, Oct 22 — counting back 14 days from when your next period is due (Thu, Nov 5). Ovulation often shifts a day or two from cycle to cycle, so treat this as the middle of a range rather than an exact date.
Your fertile window is Oct 17 – 22 (6 days). The best days are Oct 20 – 22, the two days before ovulation and ovulation day itself. Pregnancy is very unlikely more than a day after ovulation, because an egg survives only about 12 to 24 hours.
Yes — today is in your fertile window. In a classic study of couples trying to conceive, sex on this day of the cycle led to pregnancy about 16% of the time.
Take a home pregnancy test on or after Thu, Nov 5, the day your next period is due. Tests detect hCG, which rises only after a fertilized egg implants — usually 6 to 12 days after ovulation — so testing before your missed period often reads negative even if you are pregnant. If it's negative and your period still hasn't come, test again in a few days.
If you conceive in this window, your estimated due date is July 15, 2027 — 266 days after ovulation, the same as 280 days from your last period in a 28-day cycle. Only about 1 in 20 babies arrives on the due date itself; most come within two weeks either side.
In your 20s and early 30s the chance of pregnancy is about 25% to 30% each cycle; by 40 it is about 10% or less. Enter your age above for guidance on when to see a doctor.
If your cycles vary by more than a few days, tick "My cycles vary" and enter your shortest and longest cycles. The calculator then widens the window to cover both, instead of assuming every cycle is 28 days. Cycles that are often shorter than 21 days or longer than 35 are worth mentioning to a doctor.
Chance of Pregnancy on Each Fertile Day
Your next fertile window, with the chance of pregnancy from sex on each day, as measured in Wilcox et al., New England Journal of Medicine, 1995.
- Sat, Oct 175 days before ovulation10%
- Sun, Oct 184 days before ovulation16%
- Mon, Oct 193 days before ovulation14%
- Tue, Oct 202 days before ovulation27%
- Wed, Oct 211 day before ovulation31%
- Thu, Oct 22Estimated ovulation day33%
Those figures come from healthy couples in their 20s and 30s; chances are lower with age and vary from couple to couple. Having sex every one to two days through the window gives nearly the best possible odds — there's no need to time it to the hour.
Your Next Six Cycles
| Period | Fertile window | Ovulation | Next period / test | Due date if pregnant |
|---|---|---|---|---|
| Oct 8 – 12 now | Oct 17 – 22 | Thu, Oct 22 | Thu, Nov 5 | July 15, 2027 |
| Nov 5 – 9 | Nov 14 – 19 | Thu, Nov 19 | Thu, Dec 3 | August 12, 2027 |
| Dec 3 – 7 | Dec 12 – 17 | Thu, Dec 17 | Thu, Dec 31 | September 9, 2027 |
| Dec 31 – Jan 4 | Jan 9 – 14 | Thu, Jan 14 | Thu, Jan 28 | October 7, 2027 |
| Jan 28 – Feb 1 | Feb 6 – 11 | Thu, Feb 11 | Thu, Feb 25 | November 4, 2027 |
| Feb 25 – Mar 1 | Mar 6 – 11 | Thu, Mar 11 | Thu, Mar 25 | December 2, 2027 |
Projections further ahead are less certain: small differences in cycle length add up month after month. Update the calculator with the start date of each new period.
How to Confirm You're Ovulating
These detect the hormone surge that comes 24 to 36 hours before ovulation. Store-brand strips bought in bulk online often cost well under a dollar each. Start a few days before your window opens and test at the same time each afternoon.
Taken first thing every morning with a basal thermometer, your temperature rises about half a degree Fahrenheit after ovulation and stays up until your next period. It confirms ovulation after the fact, so it's most useful for learning your pattern over a few cycles.
In the days before ovulation, mucus becomes clear, slippery and stretchy — like raw egg white. That is the body's own sign that the fertile window is open, and it costs nothing to watch for.
What to Do in Your Situation
Fertility specialists recommend seeing a doctor after 6 months of trying from age 35, and right away after 40, rather than waiting a full year. Ask about a preconception visit before you start: checking thyroid function, medications and folic acid (400 micrograms a day) makes a difference whatever your age.
In perimenopause, cycles often get shorter, then irregular, and some cycles have no ovulation at all — which makes calendar predictions unreliable. Pregnancy is still possible until you have gone 12 months in a row without a period, so keep using birth control until then if you don't want to conceive.
Don't rely on a calculator. Calendar-only methods are among the least reliable forms of birth control in typical use, because ovulation can shift without warning. If you want to use fertility awareness, learn a method that combines temperature and mucus signs from a trained instructor, or talk with a clinician about other options.
Cycles regularly shorter than 21 days or longer than 35, or periods that skip months, can point to thyroid problems, PCOS or other treatable conditions that also affect fertility. They're worth checking with a doctor whether or not you're trying to conceive.
How This Calculator Works
Your next periods are projected forward from the first day of your last period using your average cycle length. Ovulation is estimated by counting back your luteal phase — 14 days unless you change it — from the day your next period is due. The fertile window is the five days before ovulation plus ovulation day, and the most fertile days are the last three. In a 2019 study of more than 600,000 cycles, the average luteal phase was closer to 12 or 13 days, so the calendar also shades in a few "possible" days on either side.
With "My cycles vary" turned on, the window follows the calendar-method rule: from cycle day (shortest cycle − 18) to cycle day (longest cycle − 11). Due dates are 266 days after estimated ovulation. Chances of conception by day come from Wilcox, Weinberg and Baird, NEJM 1995.
This calculator gives estimates for planning only and is not medical advice or a method of birth control. Ovulation can vary from cycle to cycle, especially with stress, illness, breastfeeding, recent hormonal birth control or approaching menopause. Talk with a doctor or midwife about trying to conceive or preventing pregnancy.
Key sources: Wilcox AJ, Weinberg CR, Baird DD, New England Journal of Medicine (1995) · Bull JR et al., npj Digital Medicine (2019) · American Society for Reproductive Medicine · American College of Obstetricians and Gynecologists · Centers for Disease Control and Prevention