How to use the ovulation calculator
- Enter the first day of your last period: the first day of real bleeding, not spotting.
- Enter your average cycle length, counted from the first day of one period to the first day of the next. If it varies, use the average of your last few cycles.
- Leave the luteal phase at 14 days unless you have tracked your own, for example with ovulation tests or temperature charts.
- Read your estimated ovulation date, your fertile window, and the table for the next six cycles.
How ovulation is estimated
The luteal phase is the time from ovulation to the start of the next period. It stays fairly constant for each person, usually 12 to 14 days, while the first half of the cycle is the part that changes. That is why the calculator counts back from your next period rather than forward from the last one. With a 32-day cycle, you probably ovulate around 18 days after your period starts, not 14.
The fertile window is six days because sperm can survive up to 5 days in the body and an egg lives for about 12 to 24 hours after it is released. Studies of couples trying to conceive (Wilcox and colleagues, 1995) found that nearly all pregnancies came from sex in the six days ending on ovulation day. The highest chances were in the last three of those days.
Worked example
The calculator opens with a last period 7 days before today, a 28-day cycle and a 14-day luteal phase. On October 29, 2026, that period started on October 22, 2026.
- Next period: October 22 + 28 days = November 19, 2026
- Ovulation: November 19 − 14 days = November 5, 2026. Counting the first day of your period as day 1, that is cycle day 15
- Fertile window: October 31 to November 5
- Most fertile days: November 3 to November 5
The next cycles repeat every 28 days. The second cycle starts November 19 with ovulation on December 3, and the sixth starts March 11, 2027 with ovulation on March 25.
This is not birth control
Please don't use this calculator to avoid pregnancy. A calendar can't see what your body is actually doing, and ovulation can arrive days earlier or later than expected after stress, illness, travel, breastfeeding or a change in medication. Fertility awareness methods used for contraception combine daily signs such as basal body temperature and cervical mucus, and they need training to use well. If you don't want to get pregnant, talk to a doctor, nurse or pharmacist about reliable contraception.
Ways to confirm ovulation
| Sign | What to look for |
|---|---|
| Ovulation predictor kits | A surge in LH hormone in urine, usually 24 to 36 hours before ovulation |
| Cervical mucus | Clear, stretchy, slippery mucus in the days before ovulation |
| Basal body temperature | A small rise of about 0.3 °C (0.5 °F) after ovulation has happened |
Temperature charts only show ovulation after the fact, so they are most useful for learning your pattern over several months. Once you know your own luteal phase, enter it above for a more personal estimate.
Frequently asked questions
Do I ovulate on day 14?
Only if your cycle is about 28 days long and your luteal phase is 14 days. Counting your period's first day as day 1, that puts ovulation on day 15, 14 days before the next period. Longer cycles mean later ovulation, and shorter cycles mean earlier ovulation.
Can I get pregnant outside the fertile window?
It is unlikely on a perfectly regular cycle, but cycles are rarely perfectly regular. Ovulation can shift, so the true fertile window may not match the calculated one. That is why calendar dates alone are not a reliable way to prevent pregnancy.
What if my cycles are irregular?
The predictions become much less reliable, especially for later cycles. Ovulation tests can help you pinpoint the day. Cycles that are regularly shorter than 21 days or longer than 35 days, or that change a lot from month to month, are worth discussing with your doctor.
When should I see a doctor about getting pregnant?
If you are under 35 and have been trying for a year, or 35 or older and have been trying for six months, see your doctor. Go sooner if you have very irregular or absent periods, or a known condition that affects fertility.
Related calculators
- Period Calculator — Predict your next 6 periods and the fertile days in each cycle from your last period, cycle length and period length.
- Pregnancy Conception Calculator — Estimate your conception date and fertile window from your last period or due date, with the early pregnancy timeline.
- Due Date Calculator — Your estimated due date by Naegele's rule, adjusted for cycle length, or from a conception or IVF transfer date.
- Pregnancy Calculator — How many weeks pregnant you are, your due date, trimester and key milestones, from your last period, conception, ultrasound or IVF.
Results are estimates for general information and are not medical advice. Talk to a doctor or other qualified professional about your health. See our disclaimer.