Ovulation Calculator
Ovulation typically occurs 14 days before next period (day 14 of a 28-day cycle). Fertile window: 5 days before ovulation through ovulation day (6 days total). Egg lives 12-24 hours after release, sperm survives 5 days. Track cycle length to predict: ovulation day = cycle length - 14. For 30-day cycle, ovulation on day 16. Use basal body temperature (rises 0.5-1°F after ovulation) or ovulation predictor kits (detect LH surge 24-36 hours before) for confirmation. Irregular cycles make prediction harder.
Calculate your estimated ovulation date and fertile window based on your menstrual cycle. View a visual calendar of period days, fertile days, and ovulation across the next 6 months.
Last Menstrual Period
First day of your last period
Cycle Length (days)
Typical: 21–35 days
Period Length (days)
Typical: 3–7 days
⚠️ Important Disclaimer
- This calculator provides estimates based on average cycle patterns
- Ovulation can vary by several days even with regular cycles
- This tool should not be used as a method of contraception
- Stress, illness, travel, and lifestyle changes can affect ovulation timing
- Always consult with your healthcare provider for personalized fertility advice
How to Use
- Enter your value in the input field
- Click the Calculate/Convert button
- Copy the result to your clipboard
Frequently Asked Questions
- How is ovulation date calculated?
- Ovulation typically occurs about 14 days before your next period starts. For a 28-day cycle, that is around day 14. For a 30-day cycle, ovulation is around day 16. This calculator subtracts 14 from your cycle length to estimate the ovulation day within each cycle.
- What is the fertile window?
- The fertile window spans approximately 6 days: the 5 days before ovulation plus ovulation day itself. Sperm can survive up to 5 days in the reproductive tract, so intercourse in the days leading up to ovulation can result in pregnancy. The most fertile days are the 2-3 days before ovulation and ovulation day.
- Can I use an ovulation calculator as birth control?
- No. Ovulation calculators provide estimates based on average cycle patterns and should not be relied upon for contraception. Ovulation timing can vary due to stress, illness, travel, hormonal changes, and other factors. Consult a healthcare provider for reliable birth control methods.
- What are the signs of ovulation?
- Common ovulation signs include: changes in cervical mucus (becomes clear, stretchy, and egg-white-like), a slight rise in basal body temperature (0.4–1°F after ovulation), mild pelvic pain or cramping on one side (mittelschmerz), increased libido, and a positive ovulation predictor kit (OPK) detecting the LH surge 24–36 hours before ovulation.
- How accurate is an ovulation calculator?
- Ovulation calculators are most accurate for people with regular, predictable cycles. They estimate based on averages and may be off by several days. For more precise tracking, combine with basal body temperature charting, cervical mucus monitoring, or ovulation predictor kits. Irregular cycles make prediction less reliable.
- What affects ovulation timing?
- Many factors can shift ovulation earlier or later: stress, significant weight changes, intense exercise, illness, travel across time zones, hormonal conditions like PCOS, breastfeeding, perimenopause, and certain medications. Even with regular cycles, ovulation day can vary by a few days from month to month.