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Calculate your baby's due date from last period or ultrasound. Track pregnancy weeks, trimester, milestones, and expected delivery window with our accurate due date calculator.
Weeks 1-13
Key Milestones:
Weeks 14-27
Key Milestones:
Weeks 28-40
Key Milestones:
Our due date calculator helps you estimate when your baby will arrive using two proven methods. For the LMP (Last Menstrual Period) method, enter the first day of your last period and your average cycle length. The calculator uses Naegele's Rule to add 280 days (40 weeks) to determine your due date. For the ultrasound method, enter your ultrasound date and the gestational age measured during the scan. You can also compare both methods to see if there's any difference in the estimated due dates.
A due date is an estimate of when your baby will be born, calculated as 40 weeks (280 days) from the first day of your last menstrual period. Most babies arrive between 37-42 weeks of pregnancy, which is considered the normal range for full-term delivery. The due date serves as a reference point for tracking your baby's development and scheduling prenatal appointments. It's important to understand that this is an estimated delivery window, not a precise prediction, as natural labor can begin anytime within the full-term period.
The LMP method calculates your due date by adding 280 days to the first day of your last period. This method works best for women with regular 28-day cycles. The ultrasound method measures your baby's size to determine gestational age and calculate the due date. First trimester ultrasounds (8-13 weeks) are the most accurate, with precision within 3-5 days. If there's a significant difference (more than 7 days) between LMP and ultrasound dates, healthcare providers typically use the ultrasound date as it reflects actual fetal development.
Pregnancy is divided into three trimesters, each lasting approximately 13 weeks. The first trimester (weeks 1-13) is when all major organs form and morning sickness is common. The second trimester (weeks 14-27) is often called the "honeymoon period" with increased energy and the ability to feel baby movements. The third trimester (weeks 28-40) involves rapid baby growth and preparation for delivery. Understanding which trimester you're in helps you know what to expect and when important milestones occur.
Full term pregnancy is now classified into specific categories by the American College of Obstetricians and Gynecologists (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 best health outcomes, with fully developed lungs and brains. While babies born at 37 weeks are considered full term, research shows that each additional week in the womb provides important developmental benefits.
Several factors affect due date accuracy. Irregular menstrual cycles make LMP dating less reliable because ovulation timing varies. First-time mothers tend to deliver slightly later than the due date, while women who have given birth before may deliver earlier. Multiple pregnancies (twins, triplets) typically result in earlier delivery. Certain medical conditions, maternal age, and baby's size can also influence when labor begins. Despite these variables, the due date remains a useful tool for monitoring pregnancy progress.
Key pregnancy milestones include: First ultrasound (8-12 weeks) for dating and confirming heartbeat, end of first trimester (13 weeks) when miscarriage risk decreases significantly, anatomy scan (18-22 weeks) to check baby's development and possibly learn gender, viability (24 weeks) when baby could survive with medical help if born early, third trimester (28 weeks) when baby's brain develops rapidly, and full term (37 weeks) when baby is ready for birth. Tracking these milestones helps you prepare for each stage of pregnancy.
Contact your healthcare provider immediately if you experience severe abdominal pain, heavy bleeding, severe headaches, vision changes, decreased fetal movement after 28 weeks, or signs of preterm labor before 37 weeks (regular contractions, pelvic pressure, fluid leakage). Regular prenatal appointments are essential for monitoring your health and baby's development. If you go past your due date, your provider will schedule additional monitoring to ensure your baby's well-being and may recommend induction between 41-42 weeks.
Due date calculators provide an estimated delivery date based on your last menstrual period (LMP) or ultrasound measurements. Most babies (approximately 95%) are born within 2 weeks before or after the estimated due date, with delivery occurring naturally between 37-42 weeks of pregnancy. First trimester ultrasound (8-13 weeks) is the most accurate method for dating pregnancy, with accuracy within 3-5 days.
The due date is calculated using Naegele's Rule: add 280 days (40 weeks) to the first day of your last menstrual period. This assumes a 28-day cycle with ovulation occurring on day 14. For irregular cycles, the calculation adjusts based on your average cycle length. The formula is: LMP + 280 days = Estimated Due Date.
LMP (Last Menstrual Period) due date is calculated by adding 280 days to your last period's first day. Ultrasound due date is determined by measuring the baby's size during a scan. Ultrasound dating is more accurate, especially in the first trimester, because it measures actual fetal development rather than relying on cycle regularity. If there's a significant difference (more than 7 days), doctors typically use the ultrasound date.
Your due date may be adjusted based on early ultrasound measurements, typically performed between 8-13 weeks. If the ultrasound date differs from the LMP date by more than 7 days, your healthcare provider will likely change your due date to match the ultrasound. After the first trimester, due dates are rarely changed as later ultrasounds are less accurate for dating.
Full term pregnancy is now classified into categories: 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 best health outcomes. Most healthcare providers will not let pregnancy continue beyond 42 weeks due to increased risks.
Pregnancy is calculated from the first day of your last menstrual period, not from conception. To calculate your current week, count the number of days from your LMP to today, then divide by 7. For example, if it's been 154 days since your LMP, you're 22 weeks pregnant. Pregnancy is typically 40 weeks (280 days) from LMP.
Pregnancy is divided into three trimesters: First trimester (weeks 1-13), Second trimester (weeks 14-27), and Third trimester (weeks 28-40). Each trimester is approximately 13 weeks long. The trimester system helps track developmental milestones and typical pregnancy symptoms during each phase.
Pregnancy is 40 weeks (280 days) from the first day of your last period, which equals about 9 months and 1 week. The confusion arises because pregnancy is measured from LMP, not conception. Actual fetal development is about 38 weeks (from conception), but medical dating uses 40 weeks from LMP for consistency and ease of calculation.
If you don't remember your last period date, your healthcare provider will use ultrasound to date your pregnancy. Early ultrasound (before 13 weeks) is highly accurate for determining gestational age. The ultrasound measures the baby's size (crown-rump length) to estimate how far along you are and calculate your due date.
No, stress or diet cannot change your actual due date, which is determined by when conception occurred. However, these factors can affect when labor begins. Babies come when they're ready, typically between 37-42 weeks. While you can't change your due date, maintaining good health, managing stress, and following your doctor's advice can support a healthy pregnancy.
Going past your due date is common - about 50% of first-time mothers deliver after their due date. Your healthcare provider will monitor you more closely after 40 weeks, typically with non-stress tests and ultrasounds to check baby's well-being and amniotic fluid levels. Most providers will recommend induction between 41-42 weeks to reduce risks associated with post-term pregnancy.
For IVF pregnancies, the due date is calculated from the embryo transfer date. For a Day 3 embryo transfer, add 263 days to the transfer date. For a Day 5 blastocyst transfer, add 261 days. IVF due dates are highly accurate because the exact conception date is known. Your fertility clinic will provide your official due date.
This calculator provides an estimated due date using standard obstetric methods. The due date represents the expected delivery time at 40 weeks, though normal full-term delivery occurs between 37-42 weeks of pregnancy. First trimester ultrasound (8-13 weeks) is the most accurate method for dating pregnancy, with accuracy within 3-5 days. Always consult with your healthcare provider for personalized medical advice and accurate pregnancy dating. This tool is for educational purposes and not a substitute for professional medical care or prenatal monitoring.