Ovulation Date Calculator & Ovulation Calendar
Your ovulation date is about 14 days before your next period starts. Add your cycle length to the first day of your last period, then count back 14 days. On a 28-day cycle that is cycle day 15, and your fertile window runs from 5 days before ovulation through ovulation day.
Find your ovulation date
Everything is calculated inside your browser. Nothing you enter is saved or sent anywhere.
Count from day 1 of one period to day 1 of the next. Not sure? 28 is the textbook average, though most of us are a little different.
Not sure? Keep 14, the standard. Many of us run a day or two shorter, and this one setting can move your date.
Period lengthYour cycle orbit will appear here
Choose your dates above and tap the button. You will get your ovulation date, fertile window, a day-by-day chance of pregnancy, and a six-cycle ovulation calendar you can add to your phone.
Your ovulation forecast
The Fertility Tide: your odds, day by day
Percentages are from 625 cycles in 217 women whose ovulation day was confirmed by hormone testing (Wilcox et al., NEJM). A calendar estimate is less exact than a lab-confirmed day, so treat these as a guide.
What if my luteal phase is different?
Tap a number to see how your ovulation date moves if your luteal phase is shorter or longer.
Your Ovulation Calendar for the Next Six Cycles
Once you run the calculator, your ovulation calendar fills in below. Jade days are fertile, the bright jade days are your peak days, the gold day is estimated ovulation, and a rose bar under a date marks an expected period day. Tap any date to see its cycle day and conception chance.
Month
Your next six cycles at a glance
| Cycle | Period starts | Fertile window | Ovulation | Test day |
|---|
Future cycles assume your cycle length stays the same. Real cycles drift, so come back and enter your new period date each month for a fresh forecast.
How This Ovulation Date Calculator Works
I built this ovulation date calculator around one idea that many calculators skip: ovulation is tied to the end of your cycle, not the middle. The stretch between ovulation and your next period, your luteal phase, is far steadier from month to month than the first half of your cycle, which is where most of the variation lives. So instead of guessing “day 14,” I count back from your next period.
- Find your next period. I add your cycle length to the first day of your last period.
- Subtract your luteal phase. Fourteen days is the standard, and you can change it. The result is your estimated ovulation date.
- Open your fertile window. Sperm can survive up to five days and the egg lasts about a day, so your window runs from five days before ovulation through ovulation day.
- Project six cycles forward. That is what turns the calculator into an ovulation calendar you can plan around.
A worked example
Your period started October 1 and your cycles run 28 days. Your next period is due October 29. Subtract 14 days and you get October 15 as your estimated ovulation date, which is cycle day 15. Your fertile window is October 10 to October 15, and a pregnancy test is most reliable from October 29.
You may have read that ovulation happens on “day 14.” Counting conventions differ by a day, and both describe the same estimate. The natural variation from cycle to cycle is much bigger than that one day, which is exactly why I show you ranges, odds and a calendar instead of a single number.
Looking back: when did I ovulate?
This works in reverse too. Enter the first day of a past period and your usual cycle length, and the calendar shows when you most likely ovulated that month. If you are trying to work out whether a particular day was fertile, pair that estimate with your basal body temperature chart for confirmation.
Your Fertile Window, Day by Day
This is the part I wish every calculator showed. Your fertile window is not six equally good days. The best-known data come from a study of 625 cycles in 217 women whose ovulation day was identified with urinary hormone tests. Here is what they found for sex on each day around ovulation.
| Day of sex | Chance of pregnancy | What is happening |
|---|---|---|
| 5 days before | 10% | The window opens. Sperm that arrive now can wait for the egg. |
| 4 days before | 16% | Odds climb as your cervical mucus becomes more sperm-friendly. |
| 3 days before | 14% | Still fertile, and a good day to be intentional about timing. |
| 2 days before | 27% | Your odds nearly double. This is the first peak day. |
| 1 day before | 31% | One of the two highest-chance days. |
| Ovulation day | 33% | The highest single-day chance in the study. |
| 1 day after | About 0% | The egg lives for roughly a day, so the window has closed. |
Notice how steeply the odds rise in the last three days. If you can only be intentional about a few days a month, the two days before ovulation and ovulation day are the ones to protect. These figures apply when the ovulation day is known, so with a calendar estimate I would treat them as a guide and cover a day on either side.
Ovulation Date by Cycle Length
People search for “ovulation calculator for a 35 day cycle” or “when do I ovulate on a 24 day cycle” because the usual advice is written for a 28-day cycle. Here is the same calculation for every cycle length from 21 to 40 days, using a 14-day luteal phase and then a 12-day luteal phase for comparison. All days are counted from day 1 of your period.
| Cycle length | Next period starts | Ovulation (14-day luteal) | Fertile window | Ovulation (12-day luteal) |
|---|---|---|---|---|
| 21 days | Day 22 | Day 8 | Days 3 to 8 | Day 10 |
| 22 days | Day 23 | Day 9 | Days 4 to 9 | Day 11 |
| 23 days | Day 24 | Day 10 | Days 5 to 10 | Day 12 |
| 24 days | Day 25 | Day 11 | Days 6 to 11 | Day 13 |
| 25 days | Day 26 | Day 12 | Days 7 to 12 | Day 14 |
| 26 days | Day 27 | Day 13 | Days 8 to 13 | Day 15 |
| 27 days | Day 28 | Day 14 | Days 9 to 14 | Day 16 |
| 28 days | Day 29 | Day 15 | Days 10 to 15 | Day 17 |
| 29 days | Day 30 | Day 16 | Days 11 to 16 | Day 18 |
| 30 days | Day 31 | Day 17 | Days 12 to 17 | Day 19 |
| 31 days | Day 32 | Day 18 | Days 13 to 18 | Day 20 |
| 32 days | Day 33 | Day 19 | Days 14 to 19 | Day 21 |
| 33 days | Day 34 | Day 20 | Days 15 to 20 | Day 22 |
| 34 days | Day 35 | Day 21 | Days 16 to 21 | Day 23 |
| 35 days | Day 36 | Day 22 | Days 17 to 22 | Day 24 |
| 36 days | Day 37 | Day 23 | Days 18 to 23 | Day 25 |
| 37 days | Day 38 | Day 24 | Days 19 to 24 | Day 26 |
| 38 days | Day 39 | Day 25 | Days 20 to 25 | Day 27 |
| 39 days | Day 40 | Day 26 | Days 21 to 26 | Day 28 |
| 40 days | Day 41 | Day 27 | Days 22 to 27 | Day 29 |
Short cycles (21 to 25 days)
If your cycle is 24 days, you ovulate around cycle day 11 and your fertile window can begin on day 6. That overlaps with the end of many periods, which is why short-cycle moms are so often surprised that they can conceive right after bleeding stops.
Average cycles (26 to 32 days)
A 30-day cycle ovulates around day 17 and a 32-day cycle around day 19. Both are completely normal, and both put you well past the day-14 mark that most apps assume.
Long cycles (33 to 40 days)
On a 35-day cycle I estimate ovulation around day 22, with a fertile window from day 17. Long cycles are also the ones where a calendar is least reliable, because ovulation may arrive later in some months than in others. This is where ovulation tests earn their place.
Ovulation Calculator for Irregular Periods
If your cycle is a moving target, please do not feel that you are doing something wrong. In a study of more than 600,000 cycles, only about 13% were exactly 28 days, and the average follicular phase lasted nearly 17 days. A 2024 study that followed 53 women for a year found that the luteal phase is not predictably 13 to 14 days, and that more than a quarter of cycles had a luteal phase under 10 days.
That is why the Irregular cycles tab works differently. You enter your shortest and longest cycle from the last 6 to 12 months, and I calculate the earliest and latest days ovulation could realistically fall. Your fertile window then stretches to cover that whole range, and the lilac striped days on your calendar show where it falls. The window is wide on purpose. It is honest about what a calendar can and cannot know.
Using an Ovulation Test With This Calculator
Ovulation predictor kits (OPKs) detect the LH surge that happens before an egg is released, and ovulation usually follows in about 24 to 36 hours. My approach is to let the calendar tell you when to start testing and let the test tell you when to act:
- Begin testing on the first day of the fertile window shown above.
- Test at about the same time every day, and avoid drinking a lot of fluid beforehand.
- When you get your first positive, switch to the From an OPK result tab and enter that date. I estimate ovulation for the day after, and your calendar and next-period date update to match.
- Plan sex on the day of the positive test and the day after.
Signs of Ovulation Your Body Gives You
Your body leaves clues, and learning to read them makes any calculator more accurate.
Cervical mucus
Around ovulation, cervical mucus becomes clear, slippery and stretchy, a lot like raw egg white. It is the most sperm-friendly mucus you will have all month, and it often appears a few days before ovulation.
Basal body temperature
Your resting temperature rises slightly after ovulation and stays up until your period. Because the rise happens after the egg is released, a BBT chart confirms ovulation in hindsight rather than predicting it. Over a few cycles, though, it shows you your own pattern, and that pattern is gold for fine-tuning your luteal phase setting in this calculator.
A one-sided pelvic twinge
Some women feel a brief ache or twinge on one side of the lower abdomen around ovulation. It is common and usually mild, but severe or lasting pain is not normal and deserves a call to your clinician.
After Ovulation: Testing and Due Dates
Once you have ovulated, the two-week wait begins. Implantation typically happens about 6 to 12 days after ovulation, and the most reliable time to take a home pregnancy test is the day your period is due or later. Some sensitive tests can pick up a pregnancy a few days earlier, but a negative result that early can be wrong.
If you do conceive, your due date is roughly 266 days after ovulation, which is the same 40-week pregnancy counted from a conception date. The results panel shows that date as a preview, and the Due Date Calculator and Implantation Calculator can take you through the next steps.
When an Ovulation Calculator Can Mislead You
- After having a baby. You can ovulate before your first postpartum period, even while breastfeeding or pumping, so give your cycles a few months to settle before relying on a calendar.
- After stopping hormonal contraception. Cycles can take time to find their rhythm, and the first ovulation can arrive earlier or later than expected.
- PCOS and other cycle conditions. If ovulation is infrequent or unpredictable, a calendar will be unreliable, and testing and medical guidance matter more.
- Stress, illness, travel and big routine changes. Any of these can delay ovulation in a given month.
- Perimenopause. Cycle length often becomes more variable in the years before menopause.
When I Would Talk to a Doctor
Please do not wait too long if something feels off. ACOG advises an evaluation after 12 months of trying if you are under 35, and after 6 months if you are 35 or older. I would reach out sooner if your cycles are shorter than 21 days or longer than 35 days, if your periods have stopped, if you have severe pelvic pain, or if you already know you have PCOS, endometriosis or a history of pregnancy loss. You deserve answers, and early support makes a real difference.
Ovulation Date Calculator FAQs
How do I calculate my ovulation date?
Add your cycle length to the first day of your last period to find when your next period is due, then subtract your luteal phase, which is 14 days for most calculators. If your last period began on October 1 and your cycles run 28 days, your next period is due October 29 and you would ovulate around October 15. This calculator does the maths for you and lets you change the luteal phase if yours runs shorter or longer.
How accurate is an ovulation date calculator?
A calendar estimate is a very good starting point, but it is not a lab result and it can be off by a few days. In a study of more than 600,000 tracked cycles, only about 13% of cycles were exactly 28 days, and a 2024 study of 694 cycles concluded that the luteal phase is not predictably 13 to 14 days long. If your cycles vary, use the irregular mode and confirm with ovulation tests or basal body temperature.
What is the difference between an ovulation calendar and an ovulation calculator?
An ovulation calculator gives you the dates, such as your estimated ovulation day, fertile window and next period. An ovulation calendar lays those dates out across the months so you can see them next to your real life. This page does both: the calculator at the top feeds a six-cycle ovulation calendar that you can print or add to Google Calendar, Apple Calendar or Outlook.
When do I ovulate if my cycle is 24, 30, 32 or 35 days long?
With a standard 14-day luteal phase, a 24-day cycle ovulates around cycle day 11, a 30-day cycle around day 17, a 32-day cycle around day 19 and a 35-day cycle around day 22. Your fertile window is the five days before those days plus ovulation day itself. The table in this guide lists every cycle length from 21 to 40 days.
Can I use this ovulation calculator if my periods are irregular?
Yes. Switch to the Irregular cycles tab and enter your shortest and longest cycle from the last 6 to 12 months. The calculator then shows a possible ovulation range and a wider fertile window instead of a single date. With very unpredictable cycles, ovulation tests give you far better information than any calendar.
Does the length of my luteal phase change my ovulation date?
Yes, day for day. A shorter luteal phase means you ovulate later in your cycle, and a longer one means earlier. On a 28-day cycle, a 14-day luteal phase puts ovulation around cycle day 15, while a 12-day luteal phase moves it to around cycle day 17. Use the luteal phase buttons or the what-if row in your results to see how much your date moves.
How many days after my period starts do I ovulate?
On a 28-day cycle with a 14-day luteal phase, ovulation falls about 14 days after your period begins, which is cycle day 15. In real life it varies a lot. In a large study of app-tracked cycles, the average follicular phase lasted about 17 days, which is one reason I never assume that everyone ovulates on day 14.
What are the best days to get pregnant?
The two days before ovulation and ovulation day itself. In the Wilcox study, the chance of pregnancy from sex on those three days was roughly 27%, 31% and 33%, compared with about 10% five days before ovulation and close to zero the day after. Sex every 1 to 2 days across your fertile window covers you even if your estimate is off by a day.
When should I start using ovulation tests?
Start on the first day of the fertile window this calculator shows you, and test at about the same time each day. A positive result means your LH surge has started, and ovulation usually follows within about 24 to 36 hours. You can enter that positive date on the From an OPK result tab for a tighter estimate.
How do I know that I have actually ovulated?
An ovulation test shows the surge that comes before ovulation, but it does not prove an egg was released. A sustained rise in basal body temperature for about three days afterwards is a good at-home sign, and a clinician can confirm ovulation with a mid-luteal progesterone blood test, usually around 7 days after ovulation.
Can I get pregnant right after my period ends?
Yes, especially with a short cycle. Sperm can survive up to 5 days, so on a 21 to 24 day cycle the fertile window can start while you are still bleeding or just after. That is why the calendar can show fertile days that overlap with your period.
Can I use an ovulation calculator as birth control?
No. Cycles change from month to month, and a calendar cannot know when you will actually ovulate. If you want to avoid pregnancy, please talk with your clinician about a method that is designed for that.
Can I ovulate before my first period after having a baby?
Yes. Ovulation can return before your first postpartum period, including while you are breastfeeding or pumping, so a missing period does not prove that you are not fertile. Once your cycles return, an ovulation calculator becomes useful again, but give it a few cycles to settle.
When should I talk to a doctor about ovulation?
If you have been trying for 12 months and you are under 35, or for 6 months if you are 35 or older, ask for an evaluation. See your clinician sooner if your cycles are shorter than 21 days or longer than 35 days, if your periods have stopped, or if you have severe pelvic pain or known conditions such as PCOS or endometriosis.
More Maternal Health Calculators
Sources
- Wilcox AJ, Weinberg CR, Baird DD. Timing of sexual intercourse in relation to ovulation. N Engl J Med. 1995;333:1517-21. View source
- Bull JR, Rowland SP, Scherwitzl EB, et al. Real-world menstrual cycle characteristics of more than 600,000 menstrual cycles. npj Digital Medicine. 2019;2:83. View source
- Henry, Shirin, Goshtasebi, Prior. Follicular and luteal phase length variability in a one-year cohort of 53 women (694 cycles). Human Reproduction. 2024;39(11):2565. View source
- Office on Women’s Health (womenshealth.gov). Ovulation calculator and menstrual cycle information. View source
- American College of Obstetricians and Gynecologists (ACOG). Patient resources on fertility and menstrual cycles. View source