š Due Date Calculator - When Will Your Baby Arrive?
Discover your estimated due date and track your pregnancy journey week by week with our medically-accurate calculator based on Naegele's Rule.
What Is a Due Date Calculator and Why Does It Matter?
A due date calculator is a medical tool that estimates when your baby is most likely to be born. Also known as the Estimated Date of Delivery (EDD) or Estimated Date of Confinement (EDC), your due date is calculated by adding 280 daysāor 40 weeksāto the first day of your last menstrual period (LMP). This method, called Naegele's Rule, has been used in obstetrics for over 200 years and remains the standard approach for initial pregnancy dating.
Knowing your due date is more than just marking a day on the calendar. It's a critical piece of information that guides your entire prenatal care journey. Your healthcare provider uses your due date to schedule important tests and screenings at specific gestational ages, monitor your baby's growth and development, and determine the optimal timing for delivery if medical intervention becomes necessary. Understanding your timeline also helps you prepare emotionally, logistically, and practically for your baby's arrival.
While the due date is called an "estimate" for good reasonāonly about 5% of babies arrive exactly on their predicted dateāit provides an invaluable framework for tracking pregnancy milestones. Most babies are born within a two-week window on either side of the due date, and a pregnancy is considered full-term anywhere from 37 to 42 weeks. Our calculator uses the same medical standard employed by obstetricians worldwide, giving you a trustworthy starting point for this incredible journey.
Whether you've just gotten a positive pregnancy test or are planning ahead, calculating your due date is one of the first and most exciting steps in pregnancy. It transforms abstract hope into a tangible timeline, allowing you to visualize when you'll meet your little one and begin counting down the weeks with anticipation.
How to Use Our Simple Due Date Calculator
Our calculator offers two methods to estimate your due date, depending on what information you have available:
Method 1: Calculate from Last Menstrual Period (LMP)
- Enter the first day of your last menstrual period: This is the first day you noticed full menstrual bleeding (not spotting). This is the most common method used by healthcare providers.
- Click "Calculate Due Date": The calculator will add 280 days to find your estimated delivery date.
Method 2: Calculate from Conception Date
- Enter your known or estimated conception date: If you know when you ovulated or conceived (for example, if you used IVF or fertility tracking), enter that date.
- Click "Calculate Due Date": The calculator will add 266 days to find your estimated delivery date.
š” Your privacy is protectedāall calculations happen in your browser, and we never store your data.
Your Pregnancy Timeline
Understanding Your Due Date Results
Once you submit your information, our calculator will provide you with a comprehensive pregnancy timeline:
š Your Estimated Due Date (EDD)
This is the dateā40 weeks from your LMP or 38 weeks from conceptionāwhen your baby is most likely to arrive. Remember that this is an estimate, and it's completely normal for labor to begin up to two weeks before or after this date.
š¤° Your Current Week of Pregnancy
If you're already pregnant, we'll show you how many weeks and days pregnant you are right now. Pregnancy is measured from the first day of your last period, so you're considered "2 weeks pregnant" at the moment of conception.
š Your Trimester Breakdown
We'll show you the dates for each of the three trimesters:
- First Trimester (Weeks 1-13): A time of rapid development and early pregnancy symptoms.
- Second Trimester (Weeks 14-27): Often called the "honeymoon phase" with more energy and visible baby movement.
- Third Trimester (Weeks 28-40+): Final growth and preparation for birth.
šÆ Your Full-Term Window
According to the American College of Obstetricians and Gynecologists (ACOG), full-term is now classified as 39-40 weeks, when babies have the best outcomes. We'll show you this optimal delivery window.
Important Note: Your healthcare provider may adjust your due date after an ultrasound, especially if done in the first trimester. Ultrasound measurements of the fetus are often more accurate than LMP-based calculations, particularly for women with irregular cycles.
The Science Behind Your Due Date: Understanding Naegele's Rule
How Pregnancy Dating Works
Pregnancy dating can be confusing at first because it doesn't begin at conception. Instead, gestational age is calculated from the first day of your last menstrual period (LMP), which typically occurs about two weeks before conception. This standardized approach allows healthcare providers to have a consistent reference point, since the exact date of conception is often unknown.
Here's the timeline of a typical 28-day cycle leading to pregnancy:
- Day 1: First day of menstrual period (this becomes your pregnancy "start date")
- Days 1-5: Menstruation
- Days 6-14: Follicular phaseāthe uterine lining rebuilds and an egg matures
- Day 14: Ovulationāthe egg is released
- Days 14-15: Fertilizationāsperm meets egg (actual conception)
- Days 20-24: Implantationāthe fertilized egg attaches to the uterine wall
- Day 28+: Missed periodātime to take a pregnancy test!
By the time you miss your period and discover you're pregnant, you're already considered approximately 4 weeks pregnant, even though conception occurred only about 2 weeks earlier.
Naegele's Rule: The Medical Standard
Naegele's Rule is the formula developed in the 1800s by German obstetrician Franz Naegele. The calculation is simple:
Due Date = LMP + 280 days (or LMP + 1 year - 3 months + 7 days)
This formula assumes a 28-day menstrual cycle with ovulation on day 14. For women with longer or shorter cycles, healthcare providers may adjust the calculation. A full-term pregnancy lasts an average of 280 days (40 weeks) from the LMP, or 266 days (38 weeks) from conception.
Why Ultrasound Dating Matters
While Naegele's Rule is an excellent starting point, ultrasound datingāespecially when performed in the first trimester (before 13 weeks)āis considered more accurate. During an ultrasound, the technician measures the crown-rump length (CRL) of the embryo or fetus, which correlates closely with gestational age.
If your ultrasound-based due date differs from your LMP-based date by more than 5-7 days, your healthcare provider will typically adjust your due date to match the ultrasound. This updated date then becomes your official EDD for the remainder of your pregnancy. According to guidelines from the American College of Obstetricians and Gynecologists, first-trimester ultrasound is the most reliable method for pregnancy dating.
Understanding Full-Term and When Babies Actually Arrive
While 40 weeks is the standard reference point, "full-term" actually encompasses a range:
- Early Term: 37 weeks 0 days - 38 weeks 6 days
- Full Term: 39 weeks 0 days - 40 weeks 6 days
- Late Term: 41 weeks 0 days - 41 weeks 6 days
- Post-Term: 42 weeks 0 days and beyond
Research shows that babies born at 39-40 weeks have the lowest risk of complications. For this reason, elective inductions and scheduled cesarean sections are typically not recommended before 39 weeks unless medically necessary.
If you go past your due date, don't worryāit's very common. About 30% of pregnancies continue past 40 weeks. Your healthcare provider will monitor you closely and may recommend induction between 41-42 weeks to reduce risks associated with post-term pregnancy. You can also use our Pregnancy Test Calculator if you're still in the early stages of confirming your pregnancy.
Frequently Asked Questions About Due Dates
How is my due date calculated?
Due dates are calculated using Naegele's Rule, which adds 280 days (40 weeks) to the first day of your last menstrual period (LMP). This method assumes a 28-day cycle with ovulation on day 14. Your healthcare provider may adjust this estimate based on ultrasound measurements, especially in the first trimester when fetal size is a more accurate predictor.
How accurate is a due date?
A due date is an estimate, not an exact science. Only about 5% of babies are born on their exact due date. Most babies are born within two weeks before or after the estimated date. A full-term pregnancy ranges from 37 to 42 weeks. Your actual delivery date can be influenced by factors including genetics, first pregnancy, age, and individual variations in pregnancy length.
What if I don't know my last menstrual period?
If you don't remember your last menstrual period, you can calculate your due date using a known or estimated conception date. You can also ask your healthcare provider for a dating ultrasound, which measures the size of the fetus to estimate gestational age. First-trimester ultrasounds (before 13 weeks) are the most accurate for dating a pregnancy.
Can my due date change?
Yes, your due date may be adjusted after an ultrasound, particularly if the measurement differs from the LMP-based estimate by more than 5-7 days. Your healthcare provider will use the most accurate information available, with first-trimester ultrasounds being considered the gold standard for dating. Once established by ultrasound, the due date typically doesn't change.
What is considered full-term?
Full-term pregnancy is now divided into subcategories by ACOG: Early term (37-38 weeks), Full term (39-40 weeks), Late term (41 weeks), and Post-term (42+ weeks). Babies born at 39-40 weeks have the lowest risk of complications. Your healthcare provider will monitor you closely as you approach and pass your due date.
What happens if I go past my due date?
Going past your due date is common and usually not a concern. About 30% of pregnancies extend beyond 40 weeks. Your healthcare provider will monitor you more closely with tests like non-stress tests and amniotic fluid checks. Most providers will discuss induction between 41-42 weeks to reduce risks associated with post-term pregnancy.
Do irregular cycles affect my due date calculation?
Yes, irregular cycles can make LMP-based due date calculations less accurate because ovulation may not occur on day 14. If you have irregular cycles, a dating ultrasound is especially important. The ultrasound measures the fetus and provides a more accurate estimate of gestational age and due date than the LMP method alone.
How many weeks pregnant am I?
Pregnancy is measured from the first day of your last menstrual period, not from conception. This means you're considered 2 weeks pregnant at conception. Pregnancy lasts approximately 40 weeks or 280 days from your LMP. You can calculate your current week by counting the weeks from your LMP to today, or use our calculator which will show your gestational age.
What are pregnancy trimesters?
Pregnancy is divided into three trimesters: First trimester (weeks 1-13), Second trimester (weeks 14-27), and Third trimester (weeks 28-40+). Each trimester brings different developmental milestones for your baby and physical changes for you. Understanding which trimester you're in helps you track your baby's development and prepare for what's ahead.
Should I rely only on a due date calculator?
While our calculator provides a medically-sound estimate using Naegele's Rule, it should not replace prenatal care. Always confirm your due date with your healthcare provider, who can perform ultrasounds and other assessments. Your provider will give you the most accurate, personalized due date and monitor your pregnancy's progress throughout all three trimesters.
Trusted Pregnancy Resources
For comprehensive information about pregnancy, prenatal care, and what to expect, explore these authoritative medical sources:
ACOG - How Your Fetus Grows During Pregnancy ā CDC - Pregnancy Information ā WHO - Maternal Health ā