Ovulation Calculator
Use our ovulation calculator to plan or avoid pregnancy. Enter the first day of your last menstrual period (LMP) and your average cycle length to calculate your most likely ovulation date, the 6-day fertile window, when your next period is expected, and the estimated due date if conception occurs.
Frequently Asked Questions
How is the ovulation date calculated?
Ovulation typically occurs 14 days before the next period. The calculator estimates it as: LMP date + (cycle length − 14). For a 28-day cycle, ovulation is around day 14. For a 30-day cycle, it would be around day 16.
What is the fertile window?
The fertile window spans 6 days: the 5 days before ovulation and the day of ovulation itself. Sperm can survive up to 5 days in the fallopian tubes, so intercourse in the days leading up to ovulation can result in pregnancy.
What cycle length should I enter?
Enter your average cycle length in days. A typical cycle is 21–35 days, with 28 days being the average. If your cycles vary, use the average of your last 3–6 cycles. This calculator supports cycle lengths from 21 to 35 days.
Is this calculator accurate?
This calculator provides estimates based on the average cycle. It is most accurate for women with regular cycles. Stress, illness, weight changes, or hormonal fluctuations can shift ovulation. For confirmed ovulation tracking, use ovulation predictor kits (OPKs) or basal body temperature (BBT) charting.