Can I ovulate twice in one cycle?

Two eggs can be released, but only within about 24 hours of each other, which is how non-identical twins happen. You do not get a second fertile window later in the same cycle. Once ovulation has passed, the fertile window for that cycle is over.

How accurate is a calendar estimate?

It is a starting point. Even people with regular cycles often ovulate a few days earlier or later than the calendar says, and stress, illness or travel can shift it further. Ovulation tests or temperature charts tell you when it actually happens in your body.

Can I use this calculator to avoid pregnancy?

No. A calendar estimate misses the real ovulation day too often to be reliable contraception. Fertility awareness methods that track temperature and cervical mucus daily need training. Speak to a clinician about effective methods.

What if my cycles are irregular?

Use your average length, then look at the table of shorter and longer cycles in the tool and plan for the whole spread. If your cycles vary by more than 7 to 9 days, or often run longer than 38 days, ovulation may not happen every month. A doctor can check for causes such as thyroid problems or PCOS.

How is the due date worked out?

It is 266 days, or 38 weeks, after your estimated ovulation. That matches the usual rule of 280 days from your last period, which assumes you ovulate 14 days in. Counting from ovulation means a long cycle or a short luteal phase moves the due date as well. Once you are pregnant, an early scan gives a firmer date.

How long should we try before seeing a doctor?

ACOG suggests seeing a doctor after 12 months of trying if you are under 35, and after 6 months if you are 35 or older. See one sooner if you are over 40, have very irregular or absent periods, or know of a fertility problem in either partner.

Ovulation Calculator

Find your ovulation day and fertile window from the first day of your last period.

First day of your last period

MonthOct

Day

Year

Cycle length

days

203245

Luteal phase

days

91317

Try an example

Estimated ovulationOct 19Mon, Oct 19, 2026, day 15 of your cycle

Fertile windowOct 14 to Oct 19

Next period dueMon, Nov 2, 2026

Home test reliable fromMon, Nov 2, 2026

Due date if you conceiveJul 12, 2027

Today, Oct 28, is day 24 of this cycle, after the estimated ovulation on Oct 19. Your next period is due Nov 2, and a home test is reliable from that day. The next fertile window is Nov 11 to Nov 16.

Luteal phase

days

91317

Try an example

On the calendar

Cycle 1 starts Mon, Oct 5, 2026. Fertile days: Oct 14 to Oct 19. Estimated ovulation: Mon, Oct 19, 2026. Next period and home test day: Mon, Nov 2, 2026. Today, Wed, Oct 28, 2026, has a dot. Only the first day of each period is marked, because period length is not an input.

Working

1
Next period: last period plus cycle lengthOct 5 + 28 days = Nov 2
2
Ovulation: next period minus the luteal phaseNov 2 − 14 days = Oct 19
3
Fertile window: the 5 days before ovulation and the day itselfOct 19 − 5 days = Oct 14
4
Due date if you conceive: ovulation plus 266 days (38 weeks)Oct 19 + 266 days = Jul 12, 2027
5
Check: the luteal phase from ovulation reaches the next periodOct 19 + 14 days = Nov 2

Your next six cycles

	Ovulation	Fertile window	Test from
Oct 5, 2026	Oct 19	Oct 14 to Oct 19	Nov 2
Nov 2, 2026	Nov 16	Nov 11 to Nov 16	Nov 30
Nov 30, 2026	Dec 14	Dec 9 to Dec 14	Dec 28
Dec 28, 2026	Jan 11	Jan 6 to Jan 11	Jan 25
Jan 25, 2027	Feb 8	Feb 3 to Feb 8	Feb 22
Feb 22, 2027	Mar 8	Mar 3 to Mar 8	Mar 22

Each cycle is 28 days with ovulation 14 days before the next period. Real cycles drift, so update the start date when each period arrives.

If your cycle is shorter or longer

25 days: ovulation Oct 16, fertile from Oct 11
26 days: ovulation Oct 17, fertile from Oct 12
27 days: ovulation Oct 18, fertile from Oct 13
28 days (yours): ovulation Oct 19, fertile from Oct 14
29 days: ovulation Oct 20, fertile from Oct 15
30 days: ovulation Oct 21, fertile from Oct 16
31 days: ovulation Oct 22, fertile from Oct 17

Each extra day of cycle length moves ovulation one day later, because the luteal phase stays about the same. If your cycles vary, plan for the whole spread.

Work back from a confirmed ovulation

If an ovulation test or a temperature rise told you the day, enter it. The tool finds the cycle start that fits your cycle and luteal lengths.

Ovulation date

MonthOct

Day

Year

Cycle started: Mon, Oct 5, 2026
Next period and test day: Mon, Nov 2, 2026
Next fertile window: Nov 11 to Nov 16

How your numbers compare

Cycle length 28 daysWithin 24 to 38
Luteal phase 14 daysWithin 11 to 17
Fertile window6 days, ending at ovulation

Cycle length: FIGO normal frequency, Munro et al. (2018). Luteal phase: ASRM Practice Committee (2021). Fertile window: Wilcox, Weinberg and Baird (1995).

Before you rely on this result. This tool is for education only and is not medical advice. Clinical decisions must be made by a qualified health professional using the full clinical picture. Sources used on this page.

How it's worked out

The tool counts back from your next period, not forward from your last one. The days after ovulation (the luteal phase) are fairly steady at about 12 to 14 days. The days before ovulation vary much more. So the steady part is the better anchor:

\displaystyle \text{ovulation}

Your next period is the first day of your last period plus your cycle length. With the usual 14-day luteal phase, a 28-day cycle puts ovulation on cycle day 15, counting the first day of bleeding as day 1.

The fertile window is the five days before ovulation plus the day itself. Sperm can live up to five days inside the body, but an egg lasts only about a day. A study of 221 women by Wilcox and colleagues found no pregnancies from sex outside that six-day span.

The tool also gives a due date if you conceive this cycle. Doctors date a pregnancy 280 days from the first day of your last period, as set out in ACOG Committee Opinion 700. That rule assumes you ovulate 14 days in. The tool counts 266 days (280 minus 14) from your estimated ovulation instead. So a longer cycle or a shorter luteal phase moves the due date along with ovulation.

Worked examples

Ana: a regular 28-day cycle

Ana's last period began Oct 5, 2026. Her next one is due Nov 2. Counting back 14 days puts ovulation on Mon, Oct 19, 2026, day 15 of her cycle. Her best days to try are Oct 14 to Oct 19. If she conceives this cycle, her due date would be about Jul 12, 2027.

Open this example in the tool

Mei: a long 33-day cycle

Mei's period began Sep 20, 2026 and her cycles run 33 days. Ovulation moves later, to Fri, Oct 9, 2026, day 20. Her fertile window is Oct 4 to Oct 9. Some months her cycle is only 30 days. Then ovulation comes on Oct 6, three days sooner, so she starts trying from Oct 1 to cover both.

Open this example in the tool

Sara: a short luteal phase

Sara tracks her temperature and knows her luteal phase is 11 days. Her cycle is 26 days and began Oct 1, 2026. Ovulation is about Fri, Oct 16, 2026, with fertile days Oct 11 to Oct 16. With the default 14 days, the tool would have said Oct 13, three days too early. Her due date if she conceives moves too: 266 days after ovulation is Jul 9, 2027, not Jul 6, 2027.

Open this example in the tool

Reading your result

Your date is a best guess, not a fact. In a study of more than 600,000 cycles logged in an app, the average cycle was 29.3 days. The phase before ovulation averaged 16.9 days, not the 14 days many calculators assume.

Here is where ovulation lands for common cycle lengths, with a 14-day luteal phase:

Cycle length	Ovulation	Fertile days
24 days	Day 11	Days 6 to 11
26 days	Day 13	Days 8 to 13
28 days	Day 15	Days 10 to 15
30 days	Day 17	Days 12 to 17
32 days	Day 19	Days 14 to 19
35 days	Day 22	Days 17 to 22
38 days	Day 25	Days 20 to 25

FIGO treats cycles of 24 to 38 days as normal. A luteal phase of 10 days or less counts as short in the ASRM committee opinion. If your numbers fall outside these ranges, the tool tells you, and a doctor can check why.

Ovulation tests pick up the hormone surge 24 to 36 hours before you ovulate. A rise in waking temperature of about 0.3 to 0.5 °C (0.5 to 1 °F) shows it has already happened. Either can confirm the date the tool gives you.

Common mistakes

Counting from the last day of your period. Day 1 is the first day of real bleeding, not spotting. Starting from the end shifts every date by about five days.
Assuming day 14 for everyone. Day 14 only fits a 28-day cycle with a 14-day luteal phase. A 35-day cycle puts ovulation near day 22.
Waiting for ovulation day. The best odds come from sex in the two days before ovulation. By the time a temperature rise shows up, the window has closed.
Using it to avoid pregnancy. Calendar dates miss the real ovulation day too often to work as birth control.
Testing too early. A test taken before your period is due can read negative even when you are pregnant. Wait until the test day the tool shows.

Questions people ask

Sources

Maintained by Anil ShahUpdated October 28, 2026Checked against 11 reference values

Period CalculatorPredict your next six periods, with ranges for irregular cycles Pregnancy Due Date CalculatorDue date from last period, conception, IVF transfer or ultrasound Date Difference CalculatorDays, weeks, months and years between two dates Age CalculatorExact age in years, months and days, with totals and next birthday Countdown CalculatorLive countdown in days, hours, minutes and seconds to any date

Ovulation Calculator

On the calendar

Working

Your next six cycles

If your cycle is shorter or longer

Work back from a confirmed ovulation

How your numbers compare

How it's worked out

Worked examples

Ana: a regular 28-day cycle

Mei: a long 33-day cycle

Sara: a short luteal phase

Reading your result

Common mistakes

Questions people ask

Sources

Related calculators