Pregnancy Due Date Calculator
Estimate your baby's due date using your last menstrual period, conception date, IVF transfer date, or ultrasound measurements. See your current gestational age, trimester, progress, and upcoming milestones.
How Pregnancy Due Dates Are Calculated
A pregnancy due date is an estimate of when your baby will arrive. Most pregnancies last about 40 weeks (280 days) from the first day of the last menstrual period, though only about 5% of babies are born on their exact due date. This calculator supports five different methods so you can use whichever information you have available.
Last Menstrual Period (Naegele's Rule)
The most common method adds 280 days to the first day of your last menstrual period. This is called Naegele's rule and assumes a 28-day cycle with ovulation on day 14. If your cycles are longer or shorter than 28 days, your doctor may adjust the date. This is the same method most healthcare providers use at your first prenatal visit.
Conception Date
If you know when you conceived (or ovulated), this method adds 266 days from that date. Since conception typically occurs about 14 days after the start of your period, this arrives at the same due date as the LMP method for a standard 28-day cycle. This method is more accurate if you tracked ovulation with tests or charting.
IVF Transfer Date
For IVF pregnancies, the embryo transfer date provides the most precise starting point. A 3-day embryo transfer adds 263 days, and a 5-day blastocyst transfer adds 261 days. These calculations account for the age of the embryo at the time of transfer.
Ultrasound Measurements
If your doctor has given you a gestational age based on ultrasound measurements, this method works backward from that information to estimate your due date. First-trimester ultrasounds (before 14 weeks) are generally the most accurate for dating a pregnancy.
Understanding Your Results
The gestational age shows how far along the pregnancy is in weeks and days. The trimester indicator tells you which third of pregnancy you are in: the first trimester covers weeks 1 through 12, the second trimester weeks 13 through 27, and the third trimester weeks 28 through 40. The milestone timeline highlights important dates like the anatomy scan window, viability milestone, and when the pregnancy reaches full term at 37 weeks.
Frequently Asked Questions
How is a due date calculated from the last menstrual period?
The most common method is Naegele's rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). This assumes a 28-day cycle with ovulation on day 14. Your doctor may adjust the date based on ultrasound measurements.
What is the difference between LMP and conception date calculations?
The LMP method adds 280 days from the first day of your last period. The conception date method adds 266 days from the date of conception (ovulation). Both arrive at the same estimated due date if ovulation occurred on cycle day 14.
How does the IVF due date calculation work?
For IVF pregnancies, the due date is calculated from the embryo transfer date. A 3-day embryo transfer adds 263 days, and a 5-day (blastocyst) transfer adds 261 days. These are more precise than LMP calculations because the exact date of fertilization is known.
How accurate is an estimated due date?
Only about 5% of babies are born on their exact due date. Most arrive within a two-week window on either side. First-trimester ultrasound dating is generally accurate to within 5-7 days. The due date is a useful reference point, but a range of 37-42 weeks is considered normal for delivery.