Due Date Calculator
Estimate your baby's arrival based on LMP, ultrasound, conception, or IVF.
Comprehensive Guide to Your Pregnancy Due Date
Discovering that you are pregnant is one of life's most exciting moments. One of the first questions almost every expectant parent asks is: "When is my baby due?" knowing your estimated due date (EDD) is essential for monitoring your baby's development, scheduling prenatal care, and preparing for the arrival of your little one.
The CalculatorBudy Due Date Calculator is designed to give you an accurate estimate based on the information you have available, whether that is the first day of your last period, a known conception date, an ultrasound scan, or an IVF transfer date.
How is the Due Date Calculated?
Pregnancy mathematics can be confusing because "Day 1" of pregnancy is usually considered the first day of your last menstrual period—meaning you aren't actually pregnant for the first two weeks of your official pregnancy timeline! Here is how the different calculation methods work:
1. Last Menstrual Period (LMP)
This is the most common method used by doctors and midwives. The standard rule (Naegele's Rule) assumes a pregnancy lasts 280 days (or 40 weeks) from the first day of your last period. This calculation assumes you have a regular 28-day menstrual cycle with ovulation occurring on day 14.
If your cycle is longer or shorter than 28 days, our calculator adjusts the math accordingly. For example, if you have a 30-day cycle, your due date will likely be 2 days later than someone with a 28-day cycle.
2. Conception Date
If you have been tracking ovulation using basal body temperature or ovulation predictor kits (OPKs), you might know the exact date you conceived. In this case, the calculation adds 266 days (38 weeks) to your conception date to find your due date. This method is often more precise for women with irregular cycles.
3. Ultrasound Scan
Sometimes, the date of your last period isn't known, or your periods are very irregular. An early ultrasound (usually between 8 and 12 weeks) is the most accurate way to date a pregnancy. The sonographer measures the crown-rump length (CRL) of the fetus. If the ultrasound date differs significantly from your LMP date (usually by more than 5-7 days), your doctor may update your official due date to match the ultrasound.
4. IVF Transfer
For pregnancies achieved through In Vitro Fertilization (IVF), the due date is calculated very precisely because the exact moment of transfer is known. The calculation depends on the age of the embryo at transfer:
- Day 3 Embryos: The due date is 266 days from the transfer date, minus 3 days.
- Day 5 Blastocysts: The due date is 266 days from the transfer date, minus 5 days.
Understanding Your Pregnancy Trimesters
Your pregnancy is divided into three distinct stages called trimesters. Each trimester brings unique developments for your baby and changes for your body.
First Trimester (Weeks 1 to 12)
This is a period of rapid development. Although you might not look pregnant yet, your body is working hard. Major organs begin to form, the heart starts beating, and limbs develop. This is also when morning sickness and fatigue are most common. By the end of this trimester, the risk of miscarriage drops significantly.
Second Trimester (Weeks 13 to 26)
Often called the "golden period" of pregnancy, many women feel a burst of energy as nausea subsides. You will likely start to show a baby bump, and between weeks 18 and 22, you may have an anatomy scan to check the baby's growth (and gender, if you choose to know!). You will also begin to feel your baby move (quickening).
Third Trimester (Weeks 27 to 40+)
In the final stretch, your baby gains weight rapidly to prepare for life outside the womb. Your organs are compressed, leading to potential shortness of breath or heartburn. You will see your doctor more frequently to monitor blood pressure and the baby's position (head down is ideal). Full term is considered 37 weeks, but most first-time moms go to 40 or even 41 weeks.
Frequently Asked Questions (FAQ)
This tool provides an estimate based on standard medical conventions. However, only about 4-5% of babies are born on their exact due date. Most babies arrive within the window of two weeks before or after the date.
Doctors often establish a provisional due date based on your period. However, a "dating scan" in the first trimester is more accurate. If the baby measures significantly larger or smaller than expected based on your period, the doctor will adjust the date to ensure accurate care.
Gestational age is how far along the pregnancy is, measured in weeks and days. It starts from the first day of your last period, not the day of conception. So, when you conceive (around week 2), you are technically already considered "2 weeks pregnant" by gestational age standards.
Yes, it is very common, especially for first-time mothers. A pregnancy is not considered "post-term" until after 42 weeks. Doctors usually monitor you closely if you go past 40 weeks and may discuss induction options if you reach 41 or 42 weeks.
Disclaimer: The results provided by CalculatorBudy are for informational purposes only and should not be used as a substitute for professional medical advice. Always consult your obstetrician or midwife for clinical decisions regarding your pregnancy.