Pregnancy Calculator
The Pregnancy Calculator can estimate a pregnancy schedule based on the provided due date, last period date, ultrasound date, conception date, or IVF transfer date.
Calculate Your Pregnancy Dates
Select your preferred calculation method and enter the required information to find your due date and other important pregnancy milestones.
Pregnancy Term & Due Date
Pregnancy is a term used to describe a woman's state over a time period (~9 months) during which one or more offspring develops inside of a woman. Childbirth usually occurs approximately 38 weeks after conception, or about 40 weeks after the last menstrual period. The World Health Organization defines a normal pregnancy term to last between 37 and 42 weeks.
During a person's first OB-GYN visit, the doctor will usually provide an estimated date (based on a sonogram) at which the child will be born, or due date. Alternatively, the due date can also be estimated based on a person's last menstrual period.
Calculation Methods
Last Menstrual Period (LMP) Method
The most common method for calculating a due date is to count 40 weeks from the first day of your last menstrual period (LMP). This method assumes a regular 28-day menstrual cycle with ovulation occurring on day 14.
Conception Date Method
If you know the exact date of conception (such as from fertility tracking or assisted reproduction), the due date is calculated as 266 days (38 weeks) from the conception date.
Ultrasound Method
An ultrasound performed in the first trimester is considered the most accurate method for dating a pregnancy. Based on measurements of the embryo or fetus, the healthcare provider can determine gestational age and calculate the due date.
IVF Transfer Date Method
For pregnancies resulting from in vitro fertilization (IVF), the due date is calculated based on the age of the embryo at transfer and the date of the transfer. For a 3-day embryo transfer, count 263 days from the transfer date. For a 5-day blastocyst transfer, count 261 days.
How to Use This Calculator
- Select the calculation method that works best for your situation.
- Enter the required date(s) and information based on your selected method.
- Click the 'Calculate My Due Date' button to see your personalized pregnancy timeline.
For the most accurate results, use the ultrasound method if you have had a first-trimester ultrasound, or the IVF transfer method if you conceived through IVF.
Pregnancy Stages Explained
First Trimester (Weeks 1-13)
During the first trimester, your baby's body structure and organ systems develop. By the end of the first trimester, your baby's heartbeat can be detected and they are about 3 inches long. This is also when most pregnancy symptoms like morning sickness are strongest.
Second Trimester (Weeks 14-26)
The second trimester is often called the 'golden period' of pregnancy. Many early pregnancy symptoms subside, and you may feel more energetic. Your baby will start to move noticeably, and you'll be able to find out the baby's sex through ultrasound if you wish.
Third Trimester (Weeks 27-40)
In the third trimester, your baby continues to grow and mature. They will gain weight rapidly, and systems like lungs and brain continue to develop. You may experience increased discomfort as your body prepares for childbirth.
Frequently Asked Questions
How accurate is the due date calculation?
Due date calculations are estimates. Only about 5% of babies are born exactly on their due date. About 80% of babies are born within 10 days of their due date. First-trimester ultrasounds can provide the most accurate dating, within 3-5 days.
What if my menstrual cycles are irregular?
If your cycles are irregular, the LMP method may be less accurate. In this case, an early ultrasound or tracking ovulation can provide a better estimate. Adjust your cycle length in our calculator for a more personalized estimate.
When should I schedule my first prenatal appointment?
Most healthcare providers recommend scheduling your first prenatal appointment once you have a positive pregnancy test, typically around 8 weeks after your last menstrual period. However, if you have health concerns or a high-risk pregnancy, you may need to be seen earlier.
Can the due date change during pregnancy?
Yes, the due date can be adjusted based on ultrasound measurements, especially if performed in the first trimester. If there's a significant difference between the LMP-based due date and the ultrasound measurements, your healthcare provider might update your due date.
How is pregnancy dated in medical terms?
In medical terms, pregnancy is dated from the first day of your last menstrual period, not from the day of conception. This is why pregnancy is considered to last 40 weeks (or 280 days) even though conception typically occurs about 2 weeks into this period.
Important Notice
This calculator provides estimates based on standard formulas and is intended for informational purposes only. It is not a substitute for medical advice. Always consult with a healthcare provider for the most accurate information about your pregnancy.