Fitness & Health · Live
Predict your most
fertile window.
Find your most fertile days with our accurate ovulation calculator. Plan your pregnancy by tracking your cycle and predicting your next ovulation, with a visual calendar that highlights the 6-day window where conception is possible.
Cycle inputs
When did your last period start?
Cycles vary 21–45 days. The average is 28. The luteal phase is biologically stable at ~14 days, so the calculator counts back from your next expected period — not forward from your last one.
Next ovulation
cycle day 14
Cycle calendar
May 2026
Cycle timeline
Key dates this cycle
- Last period startedTuesday, May 5, 2026
- Fertile window opensThursday, May 14, 2026
- Peak fertility (day before ovulation)Monday, May 18, 2026
- Predicted ovulationTuesday, May 19, 2026
- Next period expectedTuesday, June 2, 2026
- Due date if you conceiveTuesday, February 9, 2027
Field guide
How ovulation prediction works.
Each menstrual cycle has two phases. The follicular phase runs from the first day of your period until ovulation and varies in length; this is what makes a 24-day cycle different from a 32-day cycle. The luteal phase runs from ovulation to your next period and is biologically stable at roughly 14 days in nearly every healthy cycle.
Because the luteal phase is constant, the most reliable way to predict ovulation is to count backward from your next expected period rather than forward from your last. The formula this calculator uses is simply:
- LMP: first day of your last menstrual period.
- cycle length: number of days from one period's first day to the next. Average is 28; normal range is 21–45.
Why the fertile window is 6 days, not 1
The egg lives only about 12–24 hours after release. Sperm, however, can survive in fertile cervical mucus for up to 5 days. That means intercourse on any of the 5 days before ovulation, plus ovulation day itself, can result in pregnancy — a six-day window.
Within that window, the day of ovulation and the day immediately before are the peak fertility days. Studies tracking conception (notably Wilcox et al., NEJM 1995) show roughly 30% per-day probability of conception during these two days for healthy couples in their 20s and early 30s.
The estimated due date
If conception occurs in this cycle, the most likely due date is simply 266 days after ovulation, equivalent to LMP + 280 days adjusted for your cycle length:
Most pregnancies actually deliver between 38 and 42 weeks. The EDD is a single best-estimate point, not a deadline.
Early signs of ovulation
How to spot ovulation in your own body.
The calendar gives you a prediction. Your body gives you the ground truth. Most people have at least one or two of the following signs that, with a few cycles of practice, become easy to recognize.
Cervical mucus changes
Around ovulation, cervical mucus becomes clear, slippery, and stretchy, often compared to raw egg white. This 'fertile mucus' helps sperm travel and survive. If you can stretch a small amount between your thumb and finger without breaking it, you're likely in your fertile window.
Basal body temperature shift
BBT, your temperature first thing in the morning before getting out of bed, drops slightly just before ovulation, then rises by 0.5–1.0°F (0.3–0.6°C) the day after, staying elevated until your next period. The shift confirms ovulation has happened.
LH surge (positive ovulation test)
A urine ovulation predictor kit (OPK) detects the luteinizing hormone surge that triggers ovulation. A positive test usually means ovulation will occur in the next 24–36 hours. Your peak fertility window.
Mid-cycle pelvic twinge (Mittelschmerz)
Roughly 1 in 5 people feel a brief, one-sided pelvic ache when an ovary releases an egg. It can last anywhere from a few minutes to a couple of days. The side often alternates from one cycle to the next.
Cervical position softens & opens
During the fertile window the cervix moves higher, softens (described as feeling 'like lips' rather than 'like a nose tip'), and the cervical os opens slightly. This is checked manually and takes some practice to track.
Increased libido & sense of well-being
A small estrogen peak just before ovulation can heighten libido, energy, and even sense of smell or skin clarity for many people. It's subtle but real, and a useful supporting signal alongside the others.
Light spotting
A tiny amount of pink or brown spotting around ovulation is normal for some people and is thought to result from the brief estrogen drop or from the follicle rupturing. It typically lasts under a day.
Breast tenderness
Rising progesterone in the days after ovulation can cause mild breast soreness or fullness, usually a 'post-ovulation' sign rather than a pre-ovulation one, but it confirms the cycle is progressing as expected.
Bloating or mild water retention
Hormonal shifts in the late follicular phase can cause noticeable bloating or a feeling of fullness in the lower abdomen for a day or two around ovulation.
Field tip
No single sign is definitive on its own. The most reliable real-world strategy is to combine the calendar prediction from this tool with at least one body sign ; fertile mucus is the easiest to learn, BBT is the most objective, and OPKs give the cleanest peak-day pinpoint. Tracked together for two or three cycles, they typically identify the ovulation day to within ±1 day.
Disclaimer. This calculator is for cycle awareness and educational use. It is not a contraceptive method, a replacement for medical advice, or a diagnostic tool. If you have irregular cycles, are over 35 and trying to conceive, or have any concerns about your fertility, please consult a qualified healthcare provider.