Health
Ovulation calculator
Estimate your fertile window, probable ovulation day, and next period with a confidence level and cycle calendar.
Main calculation
When might your fertile window occur?
Choose the type of information you have. The result is an estimate, not a guarantee or a method of contraception.
Your data is stored only in this browser using local storage. No account is created, and nothing is sent to a server.
Cycle calendar
The legend combines color and text so it does not rely on color alone. Select a day to view its details.
Complete the calculator to view the calendar.
Day details
Select a day on the calendar to view its estimated cycle phase and fertility.
Days in the fertile window
Complete the calculator to view the breakdown.
When to take a pregnancy test
Most reliable time: -
Early-detection test: -
If you test before your missed period and get a negative result, it may simply be too early.
How to interpret confidence
Confidence improves when several recent cycles are available and their lengths vary little. It decreases when cycles are long, highly variable, or the date is less certain.
Signs that may help
LH tests, cervical mucus, and basal body temperature can complement the estimate. No single sign guarantees the exact timing of ovulation.
When to seek advice
Consider consulting a specialist after 12 months of trying to conceive, or after 6 months if you are age 35 or older.
Frequently asked questions
How can I tell when I will ovulate?
Ovulation usually occurs about 12 to 14 days before your next period. This calculator estimates that date from the first day of your last menstrual period and your cycle length, but timing can vary from one cycle to another.
How long does the fertile window last?
The main fertile window includes the five days before estimated ovulation and ovulation day itself. The following day is shown only as a margin for uncertainty.
Can I use the calculator if my cycles are irregular?
Yes, but the estimate will cover a wider range and have a lower confidence level. Enter previous cycle dates or your shortest and longest cycle lengths to obtain a range.
Can this be used as birth control?
No. This tool must not be used to prevent pregnancy. If you want to avoid pregnancy, use a reliable contraceptive method and consult a healthcare professional.
When is the best time to take a pregnancy test?
Testing is generally most reliable from the first day of a missed period. An early test can be negative even if you are pregnant, so consider testing again if your period does not start.
When should I seek advice if I am trying to conceive?
Consider seeking advice after 12 months of trying without becoming pregnant, or after 6 months if you are age 35 or older. Seek advice sooner if you are over 40, have highly irregular cycles, or have significant symptoms.