Estimate your ovulation date, fertile window and next period from the first day of your last menstrual period and your average cycle length.
Enter the first day of your last menstrual period and your average cycle length. Ovulation is estimated at ~14 days before your next period; the fertile window spans the days around it.
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An ovulation calculator estimates when you're most fertile. Ovulation usually happens about 14 days before your next period, and the fertile window is the few days before and after.
Ovulation = LMP + cycle length − 14 days. The fertile window runs from 5 days before ovulation (sperm can survive that long) to about 1 day after (the egg's lifespan). The next period is due one cycle length after the LMP.
It's an estimate based on averages. Real ovulation varies with stress, illness and travel. Ovulation predictor kits and basal body temperature tracking are more precise.
Not reliably. Sperm survives several days and ovulation can shift, so the fertile window is wider than shown. Use a proven contraceptive method for birth control.