Due Date Calculator
Calculate your estimated due date and track your pregnancy progress with multiple calculation methods.
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The first day of your last period before pregnancy
Accuracy Information
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Frequently Asked Questions
Which date gives the most accurate due date (LMP, conception, or ultrasound)?
Ultrasound dating, especially when performed in the first trimester (between 6-13 weeks), provides the most accurate due date estimation with accuracy within ±3 days. Early ultrasounds measure fetal development directly rather than relying on cycle assumptions. LMP dating assumes a 28-day cycle with ovulation on day 14, which may not apply to all women, making it accurate within ±7 days. Conception date is more accurate than LMP if you know the exact date, typically within ±5 days. IVF transfer dates are very precise since the exact timing is controlled medically.
How is gestational age calculated?
Gestational age is calculated from the first day of your last menstrual period (LMP), not from conception. This means pregnancy is considered to start about 2 weeks before actual conception occurs. This system is used because the LMP date is usually more reliably known than the exact conception date. A full-term pregnancy is 40 weeks gestational age, which equals 38 weeks from conception. Gestational age is expressed in weeks and days (e.g., 12 weeks 3 days) and is used by healthcare providers to track fetal development milestones and plan prenatal care.
Medical Disclaimer
This due date calculator provides estimates for educational purposes only. Only about 5% of babies are born on their exact due date, with most births occurring within 2 weeks before or after the estimated date. Your healthcare provider may adjust your due date based on ultrasound measurements or other factors. This tool should not replace professional prenatal care or medical advice from qualified healthcare providers.
How to Use This Calculator
This due date calculator supports four different methods. Choose the one that matches your situation for the most accurate estimate:
- Last Menstrual Period (LMP): Select the first day of your last period. This is the most common method used by healthcare providers and assumes a 28-day cycle with ovulation on day 14.
- Conception Date: If you know the exact date of conception (for example, through fertility treatments or confirmed ovulation tracking), enter that date. The calculator adds 266 days (38 weeks) to estimate your due date.
- IVF Transfer Date: Enter the date of your embryo transfer and select the embryo age at the time of transfer (3-day or 5-day). The calculator works backward to determine a conception-equivalent date.
- Ultrasound Dating: Enter the date of your ultrasound and the gestational age determined by your doctor. This is often the most accurate method, especially in the first trimester.
After entering your information, the calculator will display your estimated due date, current gestational age, trimester, days remaining, and a full pregnancy milestone timeline.
Understanding How Due Dates Are Calculated
A pregnancy due date, also called the estimated date of delivery (EDD), represents the date at which a pregnancy reaches 40 weeks of gestational age. It is important to understand that only about 5% of babies are born on their exact due date. Most births occur within a two-week window around the EDD, between 38 and 42 weeks.
Naegele's Rule
The most widely used method for calculating due dates is Naegele's Rule, developed by German obstetrician Franz Karl Naegele in the early 19th century. The rule assumes a regular 28-day menstrual cycle and that ovulation and conception occur on day 14. While simple and practical, it may be less accurate for women with cycles shorter or longer than 28 days.
Trimesters Overview
Pregnancy is divided into three trimesters, each lasting approximately 13 weeks:
- First Trimester (Weeks 1-12): All major organs and body systems begin to form. This period carries the highest risk of miscarriage and is when many early symptoms like morning sickness appear.
- Second Trimester (Weeks 13-26): Often called the most comfortable period of pregnancy. The baby grows rapidly, movements become noticeable, and most women experience an increase in energy.
- Third Trimester (Weeks 27-40): The baby gains significant weight and the lungs mature. The mother may experience increased discomfort, Braxton Hicks contractions, and preparations for labor begin.
Accuracy of Due Dates
The accuracy of a due date depends on the method used. First-trimester ultrasound dating (between 6 and 13 weeks) is considered the gold standard, with accuracy within 3 to 5 days. LMP-based calculations are accurate within about 7 days for women with regular cycles. Due dates from IVF are among the most precise since the timing is medically controlled.
Due Date Formula
Naegele's Rule:
Due Date = Last Menstrual Period (LMP) + 280 days
Alternatively: LMP + 7 days - 3 months + 1 year
Worked Example
Given: First day of last menstrual period (LMP) is March 1, 2025.
Method 1 (Add 280 days): March 1 + 280 days = December 6, 2025.
Method 2 (Naegele shortcut): March 1 + 7 days = March 8. March 8 - 3 months = December 8, 2024. Add 1 year = December 8, 2025.
Estimated Conception Date: March 1 + 14 days = March 15, 2025.
Result: The estimated due date is approximately December 6, 2025, with conception estimated around March 15, 2025.
Trimester Timeline with Key Milestones
| Trimester | Weeks | Key Baby Milestones | Mother's Experience |
|---|---|---|---|
| First (1-12) | Week 4 | Implantation; neural tube forming | Missed period; positive test |
| Week 6 | Heart begins beating | Morning sickness may begin | |
| Week 8 | All major organs forming; now a fetus | Fatigue, breast tenderness | |
| Week 12 | Reflexes developing; can move | Miscarriage risk decreases | |
| Second (13-26) | Week 16 | Gender may be visible; hearing develops | May feel first movements (quickening) |
| Week 20 | Halfway point; anatomy scan | Visible baby bump; more energy | |
| Week 24 | Viability milestone; lungs developing | Glucose screening test | |
| Third (27-40) | Week 28 | Rapid brain growth; eyes open | Braxton Hicks; shortness of breath |
| Week 36 | Lungs nearly mature; gains weight | Baby drops into pelvis | |
| Week 40 | Fully developed; ready for birth | Labor signs; due date |
Important Disclaimer
This due date calculator provides estimates for informational and educational purposes only. Due dates are approximations, and the actual date of delivery can vary by several weeks. Only about 5% of babies are born on the exact estimated due date. Factors such as the accuracy of recalled dates, cycle irregularities, and individual biological variation can all affect the prediction.
This tool is not a substitute for professional prenatal care. Your healthcare provider may adjust your due date based on ultrasound measurements, physical examinations, and your health history. Always attend regular prenatal appointments and consult your obstetrician or midwife for personalized pregnancy guidance.