Pregnancy Due Date & Ovulation Calculator
Enter the first day of your last menstrual period (LMP) and your average cycle length to estimate your ovulation date, fertile window, due date, and current pregnancy week.
If you're trying to conceive, use the ovulation date and fertile window. If you're already pregnant, use the due date and gestational age.
※ Results are estimates only. Actual ovulation and delivery dates vary between individuals. Always consult a doctor for medical advice.
Naegele's Rule (Due Date)
Due date = LMP + 280 days (40 weeks 0 days)
Estimated Ovulation Date
Ovulation ≈ LMP + (cycle length − 14 days)
The luteal phase (from ovulation to the next period) stays roughly 14 days regardless of cycle length, so ovulation can be estimated by working backward from the cycle length.
Fertile Window
From 5 days before ovulation to 1 day after (sperm can survive ~5 days, the egg is viable for ~24 hours)
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How This Is Calculated
This tool uses the first day of your last menstrual period (LMP) as a starting point to estimate ovulation, your fertile window, due date, and current gestational age.
The luteal phase — the time from ovulation to the next period — stays roughly constant at about 14 days, regardless of how long your overall cycle is. That means ovulation can be estimated by subtracting 14 days from your cycle length and adding the result to your LMP. This works whether your cycle is shorter or longer than the typical 28 days.
The due date is calculated using Naegele's Rule: 280 days (40 weeks) after your LMP. This is a simple, widely used clinical estimate, though actual delivery dates commonly vary by about two weeks in either direction.
Ovulation timing and cycle length vary between individuals and can shift due to stress or health changes. Use this tool as a general reference, and consult an OB-GYN for anything related to trying to conceive or an existing pregnancy.