Pregnancy Due Date Calculator
Calculate your estimated due date from last period, conception, or IVF transfer. See current week, trimester, and days remaining.
Typical cycle is 28 days; adjust if yours differs
Only about 4% of babies arrive on their exact due date. A pregnancy is considered full-term anywhere from 37 to 42 weeks. Always confirm with a healthcare provider — ultrasound dating in the first trimester is the most reliable method.
How the calculation works
This calculator uses Naegele's rule: add 280 days to the first day of your last menstrual period (LMP) to estimate the due date. If you know the conception date, we use that plus 266 days. For IVF, we adjust for the embryo's age at transfer. The result is a gestational estimate, not a prediction of the actual birthday.
Understanding gestational age
Gestational age is counted from LMP, not conception — so "you're 4 weeks pregnant" technically means it's been 4 weeks since your last period, roughly 2 weeks since conception. This is medical convention and what all pregnancy milestones (heartbeat at 6w, first ultrasound at 8w, anatomy scan at 20w) reference.
The three trimesters
First trimester (weeks 1-12): Organ formation, most miscarriage risk, morning sickness, fatigue. Second trimester (weeks 13-26):The "golden period" — nausea usually fades, energy returns, first movements felt around 18-22 weeks, anatomy ultrasound at 20 weeks. Third trimester (weeks 27-40): Rapid growth, visible movements, increasing fatigue, preparation for birth.
When your due date might shift
A first-trimester ultrasound is the gold standard for dating — if it disagrees with your LMP-based due date by more than 5-7 days, most providers will re-set the due date to match the ultrasound. Later ultrasounds are less accurate for dating because babies grow at different rates after the first trimester.
Important reminder
This calculator is for informational use only and not a substitute for prenatal care. Always confirm dates with a healthcare provider, who can correlate with exam findings, fetal heart rate, and ultrasound measurements. If you suspect pregnancy, book a provider appointment before 10 weeks.
Frequently asked questions
How accurate is a due date from LMP?▾
Naegele's rule (LMP + 280 days) assumes a perfect 28-day cycle with ovulation on day 14. For many people, actual ovulation varies. First-trimester ultrasound dating (performed 8-13 weeks) is the most accurate method and will often adjust the due date by a few days.
What if my cycles aren't 28 days?▾
Adjust the cycle length input. If your cycles are longer (say, 32 days), ovulation likely happens on day 18 instead of day 14, which moves the estimated conception date and due date by a few days. Irregular cycles make LMP-based estimates less reliable; ultrasound is the best backup.
How do IVF dates differ?▾
IVF dates are more precise because conception is known. For a 3-day transfer, the embryo is already 3 days old, so we subtract 3 days from the transfer date to estimate 'conception'. For a 5-day transfer (blastocyst), we subtract 5. From there, we add 280 days minus 14 (LMP equivalent) to get the due date.
What's the probability of delivering on the exact due date?▾
Only about 4-5% of babies are born on their calculated due date. Around 60% deliver within a week of it, and the rest distribute across the 37-42 week full-term window. Anything from 37 to 42 weeks is considered full-term.
When should I start prenatal care?▾
As soon as you confirm pregnancy — ideally before 10 weeks. Early prenatal care includes the first ultrasound (which dates the pregnancy), baseline labs, and lifestyle guidance. If you're trying to conceive, taking a prenatal vitamin with 400-800 mcg folic acid before conception reduces neural tube defect risk.
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