Pregnancy Due Date Calculator — Calculate Your Baby's Due Date
Calculate your estimated due date (EDD) instantly using 4 proven methods: last menstrual period, conception date, IVF transfer, or ultrasound. Get your complete pregnancy timeline with trimester breakdown.
Enter your pregnancy information to get your baby's estimated delivery date, current pregnancy week, and trimester milestones. Accurate, private, and based on medical guidelines from ACOG.
Quick Facts
- ✓Full-term pregnancy lasts 40 weeks from last menstrual period
- ✓Only 5% of babies arrive on their exact due date
- ✓Early ultrasound (8-13 weeks) provides most accurate dating
- ✓Babies born between 37-42 weeks are considered full-term
Understanding Your Due Date
Your pregnancy due date, also called estimated date of delivery (EDD), is calculated as 280 days (40 weeks) from the first day of your last menstrual period (LMP). This method, known as Naegele's Rule, assumes a 28-day menstrual cycle with ovulation occurring on day 14.
While this is the most common calculation method, it's important to understand that only about 5% of babies are born on their exact due date. Most healthy pregnancies deliver anywhere between 37 and 42 weeks. Your healthcare provider may adjust your due date based on early ultrasound measurements, which are highly accurate when performed in the first trimester.
4 Calculation Methods
- Last Menstrual Period (LMP):
Most common method, adds 280 days to your LMP date
- Conception Date:
Adds 266 days from known conception or ovulation date
- IVF Transfer:
Calculates from embryo transfer date (day 3 or day 5)
- Ultrasound:
Most accurate method using early pregnancy measurements
Pregnancy Trimesters
- First Trimester:
Weeks 1-13 | Major organ development
- Second Trimester:
Weeks 14-27 | Rapid growth phase
- Third Trimester:
Weeks 28-40+ | Final development & birth preparation
Pregnancy Due Date FAQs
How do you calculate pregnancy due date?
The most common method is Naegele's Rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). Alternatively, you can calculate from conception date by adding 266 days, or use ultrasound measurements for the most accurate estimation. Each method accounts for the typical gestational period but may vary based on individual factors.
How accurate is a pregnancy due date calculator?
Due date calculators are approximately 80% accurate within 1-2 weeks of the predicted date. Only about 5% of babies are born on their exact due date, with most arriving within 2 weeks before or after. Early ultrasounds (performed before 13 weeks) provide the most accurate estimates, typically within 3-5 days, while LMP-based calculations can vary if your cycles are irregular or ovulation occurred earlier or later than expected.
What is the most accurate way to calculate due date?
The most accurate method is an early ultrasound performed between 8-13 weeks of pregnancy. This dating scan measures the crown-rump length (CRL) of the fetus and is accurate within 3-5 days. If you have regular menstrual cycles and know your exact conception or ovulation date, that method is also highly accurate. Healthcare providers typically use ultrasound measurements to confirm or adjust LMP-based due dates.
Can my due date change?
Yes, your due date may be adjusted after an early ultrasound if the measurement differs from your LMP-based date by more than 5-7 days. This is common when cycles are irregular or conception timing is uncertain. However, once your due date is established by early ultrasound (before 13 weeks), it typically doesn't change unless there are specific medical reasons. Later ultrasounds are less accurate for dating purposes.
When will I give birth if my last period was [date]?
If you know the first day of your last menstrual period, add 280 days (40 weeks) to calculate your estimated due date. For example, if your LMP was January 1, your due date would be October 8. Use our calculator above to get your exact due date, trimester breakdown, and current pregnancy week. Remember that your actual delivery may occur 2 weeks before or after this date.
What if I don't know my last menstrual period?
If you can't remember your LMP, don't worry. You can calculate your due date using your conception date (if known), IVF transfer date, or wait for an early ultrasound. Your healthcare provider can perform a dating ultrasound in the first trimester to establish an accurate due date based on fetal measurements. This is actually more accurate than LMP calculations.
How is IVF due date calculated?
IVF due dates are calculated from the embryo transfer date. For a day 3 transfer, add 263 days to the transfer date. For a day 5 transfer (blastocyst), add 261 days. IVF dating is highly accurate because the exact conception date is known. Your clinic will provide your official due date, but our calculator can give you an immediate estimate.
When does each trimester start and end?
The first trimester spans weeks 1-13, the second trimester covers weeks 14-27, and the third trimester runs from week 28 until delivery (typically week 40). Each trimester marks distinct developmental phases: the first involves major organ formation, the second brings rapid growth and movement, and the third focuses on final maturation and birth preparation.
Medically Reviewed Content
This pregnancy due date calculator is based on clinical guidelines from the American College of Obstetricians and Gynecologists (ACOG) and uses evidence-based methods for estimating delivery dates.
Sources: American College of Obstetricians and Gynecologists (ACOG), National Institute of Child Health and Human Development (NICHD), World Health Organization (WHO)