Free Fertility Tool
Ovulation Calculator
Estimate your ovulation day and most fertile days in a few simple steps. Enter the first day of your last period and your usual cycle length to see your fertile window, next period, and a cycle calendar.
- Fertile window: see the days when pregnancy is most likely.
- Three cycles ahead: plan with estimated dates for upcoming months.
- Private: calculations run in your browser. Nothing you enter is stored or sent.
This calculator is for planning only. It should not be used as a method of birth control.
Calculate your fertile window
Enter your cycle details below.
Next estimated fertile window
Estimate only, based on average cycles
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- Period
- Fertile window
- Ovulation
- Today
Upcoming cycles
These dates are estimates based on the information you entered. Ovulation can shift from cycle to cycle, even when periods are regular. This tool is not a form of birth control.
Simple steps
How to Use the Ovulation Calculator
Find your estimated fertile days in less than a minute.
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Enter your last period
Choose the first day of your most recent period, the day full bleeding started.
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Add your cycle length
Count the days from the first day of one period to the first day of the next. Use your usual average.
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See your fertile window
View your estimated ovulation day, most fertile days, next period, and a calendar for upcoming cycles.
The method
How Is Ovulation Estimated?
Ovulation is when an ovary releases an egg. It usually happens about 14 days before your next period, not necessarily on day 14 of your cycle. That is why your cycle length matters.
The time after ovulation, called the luteal phase, tends to stay fairly steady for each person. The calculator works backward from your expected next period to estimate when you may ovulate.
Your fertile window includes the five days before ovulation and the day of ovulation itself, because sperm can survive in the body for several days while the egg lives for about a day.
Good to know: stress, illness, travel, and other changes can shift ovulation. If your cycles vary a lot, treat these dates as a rough guide.
Next period
First day of last period + cycle length
For a 28-day cycle, your next period is expected 28 days after your last one started.
Ovulation day
Next period − luteal phase (usually 14 days)
For a 28-day cycle, that is around day 14. For a 32-day cycle, around day 18.
Fertile window
5 days before ovulation through ovulation day
The two days before ovulation and the day of ovulation are usually the most fertile.
Body clues
Common Signs of Ovulation
Tracking these signs alongside the calculator can help you understand your own cycle. Not everyone notices all of them.
Cervical mucus changes
Discharge often becomes clear, slippery, and stretchy, similar to raw egg white, in the days before ovulation.
Temperature rise
Basal body temperature usually rises slightly after ovulation. Charting it over a few months can show your pattern.
Positive ovulation test
Home ovulation tests detect a rise in LH hormone, which usually happens a day or so before ovulation.
Mild one-sided twinge
Some people feel brief, mild pain on one side of the lower belly around ovulation. Severe pain should be checked by a doctor.
Questions
Frequently Asked Questions
How accurate is an ovulation calculator?
An ovulation calculator gives an estimate based on average cycle patterns. It works best if your cycles are regular, but ovulation can still shift from month to month. Ovulation tests, temperature charting, and watching cervical mucus can give you more personal information.
When am I most fertile?
Your fertile window is about six days long and ends on the day of ovulation. The chance of pregnancy is usually highest in the two days before ovulation and on ovulation day itself.
Can I use this calculator to avoid pregnancy?
No. Calendar estimates are not reliable enough to use as birth control, because ovulation timing can vary. If you want to avoid pregnancy, speak with a healthcare provider about contraception options that suit you.
What if my cycles are irregular?
If your cycle length changes a lot from month to month, the calculator will be less reliable. You can still use your average cycle length as a starting point, and ovulation tests may help. Irregular periods can have many causes, so it’s worth mentioning them to your doctor.
When should I take a pregnancy test?
Home pregnancy tests are most reliable from the first day of a missed period. Testing earlier may give a negative result even if you are pregnant, so you may need to test again a few days later.
When should I talk to a doctor about trying to conceive?
A common guideline is to see a doctor if you haven’t conceived after 12 months of trying, or after 6 months if you are 35 or older. Speak to a doctor sooner if your periods are very irregular or absent, or if you have any concerns.
Health Disclaimer
This Ovulation Calculator provides educational estimates only. It does not diagnose fertility problems, confirm ovulation, or replace advice from a doctor or other qualified healthcare professional.
It is not a method of birth control. If you are trying to conceive, are having trouble getting pregnant, or have irregular or painful periods, please speak with a healthcare provider.