Due Date Calculator. See our due date pregnancy calculator which will help you determine when your newborn baby will arrive.

Due Date Calculator: Last Menstrual Period: 1 2 3 4 5 6 7 8 9 10 11 12 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 2009 2010 2011 2012 Average Length of Cycles: (22 to 45) (defaults to 28)   Estimated Conception: Estimated Due Date: Estimated Fetal Age:

You will learn your baby's estimated due date at your first prenatal visit, which is often at 8 weeks pregnant. At this appointment, your doctor will use a variety of techniques to calculate your baby's gestational age, including the date of your last menstrual period, your uterine size, and ultrasound examination.

If you haven't been to your first prenatal visit and you are too excited to wait, you can calculate your estimated due date on your own using the date of your last menstrual period. (An easier way is to use our due date calculator above) Although this method will not be as accurate as your doctor's calculation, it is a very fun and interactive way to celebrate your pregnancy.

Most women think of pregnancy as lasting nine months, but doctors and healthcare providers don't like to use months when calculating pregnancy. They use weeks, as this is considered more precise. There are always seven days in a week, but not all months will have four weeks. Some months last five weeks.

An average pregnancy lasts 40 weeks, or 280 days, although most babies are born a few weeks before or after this 40 week mark. Babies born between 37 and 42 weeks are considered full-term. Infants born before week 37 are called "preterm," and those born after 42 weeks are called "post-term."

If you are like most people, you may think that your pregnancy started the day you conceived, or when life began-the joining of the egg and sperm. This is not how doctors think. Because the estimated date of conception is often hard to pinpoint, doctors like to use the date of your last menstrual period as the start of your pregnancy.

Using the date of your last period, a common way to calculate your due date is by using "Naegele's Rule," named after the German obstetrician who devised the method over 150 years ago. This rule assumes that you have a regular 28 day menstrual cycle, with ovulation and fertilization occurring two weeks (or 14 days) after your period.

To calculate your estimated due date using Naegele's Rule, take the first date of your last menstrual period and count back three months. Add seven days to this date, and this will be your baby's due date.

For example:

• Your last menstrual period: November 16
  
  
• Subtract three months: August 16
  
  
• Add seven days: August 23
  
  
• August 23 is your estimated due date.

Naegele's Rule may be harder to use if you have irregular cycles. Some women have shorter day cycles, and other longer. If you are one of the women who does not have typical 28 day cycles, you will need to adjust your estimated due date accordingly.

For example, if you have a shorter day cycle, such as a 24 day cycle, you would subtract four days from the due date given. Instead of August 23, your estimated due date will be August 19.

If you have a longer cycle, you would add days. Say, you have a 30 day cycle, you would add two days to get the adjusted due date. Using our example, your new estimated due date would be August 25.

Remember that Naegele's Rule is not always accurate, as many babies arrive before they are due and others later than expected. Only 5 percent of babies arrive on their estimated due date. Early pregnancy bleeding (such as implantation bleeding) and use of hormonal contraceptives can also make due date calculation less accurate.

Naegele's Rule is simply a fun and exciting way to guess when your baby will arrive. Although your doctor may be more accurate in his calculation, your baby will come tumbling into the world when he or she is ready to!

Keep in mind that regular checkups with your doctor or healthcare provider will ensure that you have a safe and successful pregnancy!

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