Estimate only. Not medical advice, not for contraception.
Upcoming cycles
Estimates only, not medical advice. Do not use this calculator for contraception. Your midwife or doctor will confirm dates, usually by ultrasound.
This ovulation calculator estimates your ovulation day, fertile window and next period from the first day of your last period, your cycle length and your luteal phase. A calendar shows the coming months at a glance. It is meant for people trying to conceive and for understanding your cycle, not for preventing pregnancy.
How to use
- Choose what you know: the first day of your last period, the conception date, or the IVF transfer date and embryo age.
- For the last period, set your usual cycle length. A cycle longer or shorter than 28 days moves the due date by the same number of days.
- Read your due date, how far along you are today and your trimester. Key dates are listed below; tap any row to copy it.
- Switch to Ovulation to see your fertile window, ovulation day and next period, with a calendar for the coming months.
- Nothing is saved unless you turn on Remember on this device.
- This is an estimate, not medical advice, and it must not be used for contraception. Ovulation varies from cycle to cycle, and only about 4% of babies are born on their due date. Your midwife or doctor will confirm the dates, usually with an early ultrasound.
- Due date from the last period uses Naegele’s rule (first day of the last period + 280 days), adjusted by your cycle length minus 28 days. From conception it adds 266 days; for IVF it adds 263 days after a day-3 transfer or 261 days after a day-5 transfer.
- Pregnancy weeks are counted from the first day of the last period, so “week 6” is about 4 weeks after conception.
- Ovulation is estimated as the next period minus the luteal phase (usually 12–14 days). The fertile window is the 5 days before ovulation plus the day of ovulation and the day after.
- Milestone timings are typical schedules and differ between countries and clinics.
How ovulation is estimated
Ovulation is counted backwards from the next period: next period minus the luteal phase, which is usually 12 to 14 days. In a 28-day cycle with a 14-day luteal phase, ovulation comes about 14 days after the period starts; in a 32-day cycle, about 18 days after. If you know your luteal phase from tracking, enter it for a closer estimate.
The fertile window is the five days before ovulation, the day of ovulation and the day after, because sperm can survive up to about five days while the egg lives for about one day.
Limits of a calendar method
Ovulation varies from cycle to cycle, even in regular cycles, and stress, illness or travel can shift it. Ovulation tests, basal body temperature and cervical mucus give more direct signals. See a doctor if you have been trying for 12 months without success, or 6 months if you are over 35.
Results are estimates for information, not medical advice, and must not be used for contraception. Your midwife or doctor will confirm dates, usually with an early ultrasound. Nothing is saved unless you turn on Remember on this device.
Frequently asked questions
When do I ovulate?
Usually 12 to 14 days before your next period. With a 28-day cycle that is about 14 days after your period starts.
What is the fertile window?
The five days before ovulation, the day of ovulation and the day after. Pregnancy is most likely from intercourse in the two or three days before ovulation.
Can I use this to avoid pregnancy?
No. Ovulation timing varies and calendar estimates are not reliable contraception. Use a proven method if you need to prevent pregnancy.
What is the luteal phase?
It is the time from ovulation to the next period, usually 12 to 14 days and fairly constant for each person. Cycle length differences mostly come from the phase before ovulation.
When is my next period due?
The first day of your last period plus your cycle length. The calculator shows it along with the following cycles on the calendar.