Ovulation Calculator
Calculate your fertile window and ovulation date based on your last menstrual period. Identify your most fertile days to optimize timing for conception.
Reviewed by Daniel Agrici, Founder & Lead Developer · Editorial policy
Ovulation Calculator Formula
Ovulation Date = LMP + (Cycle Length - 14 days)
Ovulation typically occurs 14 days before the next period (the luteal phase is relatively constant at 14 days). The fertile window spans 5 days before ovulation through 1 day after, as sperm can survive up to 5 days while the egg lives 12-24 hours. Peak fertility occurs in the 2-3 days immediately before and including ovulation.
Ovulation Calculator — Worked Examples
Example 1: Standard 28-Day Cycle
Problem:Last period started March 1. Cycle length is 28 days. When is the fertile window and ovulation date?
Solution:Cycle length = 28 days\nOvulation day = 28 - 14 = Day 14\nOvulation date = March 1 + 14 = March 15\n\nFertile window starts = March 15 - 5 = March 10\nFertile window ends = March 16\nPeak fertility = March 13-15\n\nNext period = March 1 + 28 = March 29\nPregnancy test date (if conceived) = March 15 + 14 = March 29
Result:Ovulation: March 15 | Fertile Window: March 10-16 | Peak: March 13-15 | Next Period: March 29
Example 2: Longer 32-Day Cycle
Problem:Last period started February 10. Cycle length is 32 days. Calculate ovulation and fertility dates.
Solution:Cycle length = 32 days\nOvulation day = 32 - 14 = Day 18\nOvulation date = February 10 + 18 = February 28\n\nFertile window = February 23 - March 1\nPeak fertility = February 26-28\nNext period = February 10 + 32 = March 14\n\nNote: With a 32-day cycle, ovulation occurs later than with a 28-day cycle.
Result:Ovulation: February 28 | Fertile Window: Feb 23 - Mar 1 | Next Period: March 14
Ovulation Calculator — Frequently Asked Questions
When does ovulation occur during the menstrual cycle?
Ovulation typically occurs about 14 days before the start of your next period, not 14 days after your last period — this is an important distinction. For a standard 28-day cycle, ovulation occurs around day 14. For a 30-day cycle, it's around day 16. For a 26-day cycle, it's around day 12. The 'luteal phase' (time between ovulation and your next period) is relatively consistent at 14 days for most women, while the 'follicular phase' (time from period start to ovulation) can vary significantly. Ovulation involves the release of a mature egg from an ovarian follicle. The egg survives for only 12-24 hours after release, making the timing of intercourse critical for conception. Tracking ovulation helps both for trying to conceive and for natural family planning methods.
What are the signs and symptoms of ovulation?
Several physical signs can indicate ovulation is occurring or about to occur: Cervical mucus changes — it becomes clear, stretchy, and slippery (similar to raw egg whites) around ovulation, which helps sperm travel. Basal body temperature (BBT) — your resting temperature rises 0.4-1.0 degree Fahrenheit after ovulation due to progesterone; tracking daily with a BBT thermometer can confirm ovulation occurred. Ovulation pain (mittelschmerz) — about 20% of women feel a mild, one-sided lower abdominal pain or cramping during ovulation. Breast tenderness — hormonal changes may cause sensitivity. Increased libido — many women report higher sex drive around ovulation. Cervical position changes — the cervix becomes higher, softer, and more open. Ovulation predictor kits (OPKs) detect the LH surge that occurs 24-36 hours before ovulation, providing advance notice.
How can I track ovulation more accurately?
Multiple methods can improve ovulation tracking accuracy: Ovulation Predictor Kits (OPKs) detect the luteinizing hormone (LH) surge in urine 24-36 hours before ovulation — start testing a few days before expected ovulation. Basal Body Temperature (BBT) charting involves taking your temperature every morning before getting up; a sustained rise of 0.4+ degrees confirms ovulation occurred (retrospective, so best used over multiple cycles to identify patterns). Cervical mucus monitoring tracks changes from dry to sticky to creamy to clear/stretchy — the egg-white consistency indicates peak fertility. Fertility monitors (like Clearblue or Mira) measure both estrogen and LH for a wider fertile window detection. Wearable devices (like Tempdrop or Ava bracelet) continuously track temperature for more accurate BBT data. Combining multiple methods (symptothermal method) provides the highest accuracy — typically 95-99% effective at identifying ovulation.