Pregnancy Due Date Calculator

A due date, also known as the estimated date of delivery (EDD), is the approximate date when your baby is expected to be born. It's calculated as 40 weeks from the first day of your last menstrual period. However, it's important to remember that only about 5% of women deliver exactly on their due date - it's normal to give birth up to two weeks before or after this date.

Due date calculators provide an estimate based on standard pregnancy duration. Their accuracy depends on several factors:

• How regular your menstrual cycles are
• How accurately you remember the first day of your last period
• Whether you know your conception date

For greater precision, healthcare providers often use ultrasound measurements, especially in the first trimester, to confirm or adjust the due date.

Healthcare providers typically use the last menstrual period (LMP) for several reasons:

• Most women can remember when their last period started more accurately than when conception occurred
• It provides a consistent starting point for all pregnancies
• The historical method (Naegele's rule) is based on LMP
• It's easier to standardize medical guidelines using LMP

Even though pregnancy actually begins at conception (about 2 weeks after LMP), the medical convention of counting from LMP gives healthcare providers a standardized way to track pregnancy development.

These two terms measure pregnancy in slightly different ways:

When your doctor says you're "8 weeks pregnant," they're referring to gestational age, even though your baby has only been developing for about 6 weeks (fetal age).

If you have irregular periods, the LMP method of calculating your due date may be less accurate because:

• It's harder to determine when ovulation occurred
• The standard assumption of ovulation on day 14 may not apply to you
• Your cycle length can vary significantly from month to month

In this case:

• If you know your conception date, use that method instead
• Consider early pregnancy dating ultrasounds for a more accurate estimation
• Discuss with your healthcare provider about your irregular cycles

Your healthcare provider will likely use ultrasound measurements to confirm or adjust your due date if you have irregular cycles.

Yes, your due date may change during pregnancy for several reasons:

• Ultrasound Measurements: If your first ultrasound (especially in the first trimester) shows a significant difference between the estimated fetal size and what would be expected based on your LMP, your provider may adjust your due date.
• More Accurate Information: If you later remember your LMP date more accurately or realize you were using an incorrect date.
• Multiple Pregnancies: Twins and other multiples often deliver earlier than singletons, so your provider might adjust your "expected" delivery timeframe.

It's worth noting that first-trimester ultrasounds are the most accurate for dating purposes. Later ultrasounds are less reliable for changing due dates because normal variations in fetal size become more pronounced as pregnancy progresses.

Pregnancy terms are defined by specific week ranges: