Pregnancy Due Date Calculator
Calculate your estimated due date based on your last menstrual period, conception date, or IVF transfer date. Track your pregnancy week by week.
Calculate by Last Period (LMP)
When was the first day of your last menstrual period?
Average cycle is 28 days. Adjust if yours differs (20-45 days).
Calculate by Conception Date
When did conception occur?
Calculate by IVF Transfer Date
When was the embryo transfer?
Pregnancy Trimester Guide
1st Trimester (Weeks 1-12)
Major organs begin forming. Morning sickness is common. The first heartbeat can be detected around week 6. By week 12, the fetus is about 2.5 inches long.
2nd Trimester (Weeks 13-26)
Often called the "golden period." Energy returns, nausea fades. You may feel the baby move (quickening) around weeks 18-20. Gender can be identified via ultrasound.
3rd Trimester (Weeks 27-40)
The baby gains weight rapidly. Braxton Hicks contractions may begin. The baby's lungs mature. Full term is reached at week 39. Most babies arrive between weeks 38-42.
How the Due Date Calculator Works
Our pregnancy due date calculator uses three medically recognized methods to estimate your baby's arrival. Each method applies a different starting point but arrives at the same 40-week gestational period that doctors use worldwide.
Naegele's Rule (LMP Method)
The most widely used formula, developed by German obstetrician Franz Naegele in 1812. It adds 280 days (40 weeks) to the first day of your last menstrual period. This method assumes ovulation occurs on day 14 of a 28-day cycle. If your cycle length differs, the calculator adjusts the ovulation estimate accordingly. For example, a 32-day cycle shifts the due date forward by 4 days.
Conception Date Method
If you know the exact date of conception (through ovulation tracking, basal body temperature charting, or timed intercourse), this method adds 266 days (38 weeks) from conception. This is more accurate than LMP for women with irregular cycles because it bypasses the ovulation estimation step entirely.
IVF Transfer Date Method
For IVF pregnancies, the embryo age at transfer is known precisely. A Day 5 blastocyst transfer means the embryo is already 5 days old, so the calculator subtracts 5 days to find the equivalent conception date, then adds 266 days. A Day 3 cleavage embryo works the same way with a 3-day offset. This is the most accurate method available.
Pregnancy Delivery Statistics
Understanding when babies actually arrive helps set realistic expectations. Here are evidence-based statistics from the American College of Obstetricians and Gynecologists (ACOG).
Baby Size by Week (Fruit Comparison)
Your baby grows rapidly throughout pregnancy. This week-by-week size chart compares your baby to familiar fruits and vegetables.
| Week | Size | Length | Weight |
|---|---|---|---|
| 4 | Poppy seed | 0.04 in | < 1 g |
| 8 | Raspberry | 0.6 in | 1 g |
| 12 | Lime | 2.1 in | 14 g |
| 16 | Avocado | 4.6 in | 100 g |
| 20 | Banana | 6.5 in | 300 g |
| 24 | Ear of corn | 11.8 in | 600 g |
| 28 | Eggplant | 14.8 in | 1 kg |
| 32 | Squash | 16.7 in | 1.7 kg |
| 36 | Honeydew melon | 18.7 in | 2.6 kg |
| 40 | Watermelon | 20.2 in | 3.4 kg |
Pregnancy Term Classifications (ACOG)
The American College of Obstetricians and Gynecologists classifies pregnancy terms as follows. These definitions guide medical decisions about labor induction and delivery timing.
Baby's brain and lungs are still developing. Elective delivery is generally not recommended unless medically indicated.
The ideal delivery window. Baby's organs are fully mature. This is the target range for a healthy birth.
Close monitoring is recommended. Your provider may discuss induction. The placenta begins to function less efficiently.
Associated with increased risks. Induction or cesarean delivery is typically recommended to protect both mother and baby.
Frequently Asked Questions
How is the due date calculated from LMP?
The due date is calculated using Naegele's Rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). This method assumes a regular 28-day cycle with ovulation occurring on day 14. If your cycle is longer or shorter, the calculator adjusts accordingly by modifying the ovulation day estimate.
How accurate is the due date calculator?
Only about 5% of babies are born on their exact estimated due date. Most babies arrive within a 2-week window before or after the EDD. First-time mothers tend to deliver slightly later. An ultrasound in the first trimester (before 14 weeks) can provide a more accurate estimate.
How many weeks is a full-term pregnancy?
A full-term pregnancy is between 39 weeks 0 days and 40 weeks 6 days. Early term is 37 to 38 weeks 6 days. Late term is 41 weeks 0 days to 41 weeks 6 days. Post-term begins at 42 weeks. Babies born before 37 weeks are considered preterm.
What if my cycle is longer or shorter than 28 days?
If your cycle is longer than 28 days, ovulation likely occurred later, so your due date shifts forward by the difference. If your cycle is shorter, ovulation occurred earlier and your due date shifts back. For example, a 35-day cycle means ovulation around day 21 (not day 14), adding 7 extra days to the standard calculation.
What is the difference between gestational age and fetal age?
Gestational age is counted from the first day of your last period (LMP) and includes the approximately 2 weeks before conception. Fetal age (conceptional age) counts from the actual date of fertilization. Gestational age is always about 2 weeks more than fetal age. Medical professionals use gestational age as the standard.
How do I calculate my due date from IVF transfer?
For IVF pregnancies, the calculation depends on embryo type. For a Day 5 blastocyst, subtract 5 days from the transfer date to get the equivalent conception date, then add 266 days. For a Day 3 cleavage embryo, subtract 3 days. Our calculator handles both types automatically for maximum accuracy.
Can my due date change during pregnancy?
Yes. If an early ultrasound measurement differs by more than 7 days from the LMP-based estimate, your healthcare provider may adjust the due date. First-trimester ultrasounds are the most accurate for dating. Later ultrasounds are less reliable for changing the due date.
What are the chances of delivering on my due date?
About 4-5% of babies are born on their exact due date. Roughly 80% of babies are born between 37 and 41 weeks. Think of your due date as the middle of a delivery window rather than a precise target.