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🤰 Pregnancy Details
Choose your calculation method and enter your date
👶 Your Due Date
Estimated Due Date
Enter your date above
Based on Naegele's Rule — 280 days from LMP
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How is a Pregnancy Due Date Calculated?
The most common method for calculating a pregnancy due date is Naegele's Rule — add 280 days (40 weeks) to the first day of your last menstrual period. This assumes a 28-day menstrual cycle and that ovulation occurs on day 14. Our calculator adjusts for different cycle lengths automatically.
Only about 5% of babies are born on their exact due date. Most births occur within two weeks before or after the estimated due date. The due date is best understood as the midpoint of a delivery window rather than an exact date.
Different Calculation Methods
- Last Menstrual Period (LMP) — Most common method. Add 280 days to the first day of your last period. Adjusted for cycle length.
- Conception Date — Add 266 days (38 weeks) to your conception date. More precise if you know the exact date.
- IVF Transfer — For Day 5 blastocyst transfer, add 261 days. For Day 3 transfer, add 263 days.
- Ultrasound Dating — The most accurate method, especially in the first trimester. Uses the measured size of the embryo or fetus.
The Three Trimesters
- First Trimester (Weeks 1-12) — Rapid development of all major organs. Morning sickness common. Critical period for fetal development.
- Second Trimester (Weeks 13-26) — Most comfortable trimester for many women. Baby begins moving. Gender can be determined.
- Third Trimester (Weeks 27-40) — Baby gains weight rapidly. Braxton Hicks contractions begin. Preparation for birth.
⚠️ Medical Disclaimer: This due date calculator is for informational purposes only. Your healthcare provider will confirm your due date through clinical examination and ultrasound. Always follow your doctor or midwife's guidance throughout your pregnancy.
Frequently Asked Questions
How accurate is a due date calculator? +
Due date calculators provide an estimated due date (EDD) that is typically accurate within 1-2 weeks for women with regular 28-day cycles. Early ultrasound (before 12 weeks) is the most accurate method for dating a pregnancy. Only about 5% of babies are born on their exact due date — most arrive within two weeks before or after.
How many weeks is a full-term pregnancy? +
A full-term pregnancy is 39-40 weeks. Early term is 37-38 weeks, full term is 39-40 weeks, late term is 41 weeks and post term is 42 weeks or beyond. Babies born before 37 weeks are considered premature. The American College of Obstetricians and Gynecologists (ACOG) considers 39-40 weeks as the optimal time for birth.
What if my cycle is not 28 days? +
If your cycle is longer or shorter than 28 days, ovulation and conception occur at a different point in your cycle. Our calculator adjusts for cycle length — for example, if you have a 35-day cycle, ovulation typically occurs around day 21 rather than day 14. Select your actual cycle length for a more accurate due date estimate.
When can I find out the baby's gender? +
The baby's biological sex can typically be determined by ultrasound between 18-20 weeks of pregnancy during the anatomy scan. Some parents choose NIPT (non-invasive prenatal testing) blood test which can reveal gender as early as 10 weeks. Earlier ultrasounds may sometimes indicate gender but accuracy is lower before 16 weeks.
What is Naegele's Rule? +
Naegele's Rule is the standard method for calculating a pregnancy due date, named after German obstetrician Franz Karl Naegele. The rule states: take the first day of the last menstrual period, add one year, subtract three months, and add seven days. This is equivalent to adding 280 days (40 weeks) to the LMP date. It assumes a 28-day cycle and ovulation on day 14.