Pregnancy Due Date Calculator
Calculate your estimated due date, track your pregnancy week-by-week, and discover important milestones in your pregnancy journey.
Calculate Your Due Date
Choose your calculation method and enter the required date information.
How Pregnancy Due Date Calculation Works
Pregnancy is typically calculated as 40 weeks (280 days) from the first day of your last menstrual period (LMP). This method assumes a regular 28-day cycle with ovulation occurring on day 14.
Calculation Methods
LMP Method
Due Date = LMP + 280 days. This is the standard method used by most healthcare providers.
Conception Date
Due Date = Conception Date + 266 days. Used when you know the exact date of conception.
IVF Transfer
For Day 3 embryos: LMP = Transfer Date - 17 days For Day 5 embryos: LMP = Transfer Date - 19 days
Understanding Trimesters
First Trimester
Weeks 1-13: Early development, organ formation, highest miscarriage risk.
Second Trimester
Weeks 14-27: Baby's movements felt, anatomy scan, often most comfortable period.
Third Trimester
Weeks 28-40: Rapid growth, fetal development finalization, preparation for birth.
Important Note
Only about 5% of babies are born on their exact due date. Most births occur between 37-42 weeks of pregnancy. This calculator provides an estimate—always consult with your healthcare provider for accurate pregnancy dating.
Calculation History
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Understanding Pregnancy Dating and Due Dates
Calculating your estimated due date is an exciting first step in your pregnancy journey. Understanding how due dates are calculated and what they mean can help you prepare for your baby's arrival.
How Due Dates Are Calculated
The Naegele's Rule
The most common method for calculating due dates is Naegele's rule, developed in the early 1800s by German obstetrician Franz Naegele. This rule adds 280 days (40 weeks) to the first day of your last menstrual period (LMP).
The formula is: Due Date = LMP + 7 days - 3 months + 1 year
Accuracy of Due Date Calculations
LMP Method Accuracy
The LMP method assumes a 28-day cycle with ovulation on day 14. If your cycle is longer or shorter, or if you ovulate earlier or later than day 14, your actual due date may differ.
Ultrasound Dating
Early ultrasounds (before 14 weeks) can provide a more accurate due date by measuring the baby's size. Later in pregnancy, ultrasound dating becomes less accurate.
What Your Due Date Really Means
It's important to remember that your due date is an estimate, not an expiration date. Only about 5% of babies are born on their exact due date. Most full-term pregnancies deliver between 37 and 42 weeks of pregnancy.
Term Pregnancy Definitions
- Early Term: 37 weeks 0 days to 38 weeks 6 days
- Full Term: 39 weeks 0 days to 40 weeks 6 days
- Late Term: 41 weeks 0 days to 41 weeks 6 days
- Postterm: 42 weeks 0 days and beyond
Factors That Can Affect Your Due Date
- Irregular menstrual cycles
- Length of your menstrual cycle (shorter or longer than 28 days)
- Time of ovulation (earlier or later than day 14)
- First pregnancy vs. subsequent pregnancies
- Genetic factors
- Medical conditions such as diabetes or high blood pressure
Important Disclaimer
This calculator provides an estimate of your due date based on the information you provide. It is not a substitute for professional medical advice. Always consult with your healthcare provider for accurate pregnancy dating and prenatal care.