Pregnancy Due Date Calculator

An estimated due date (EDD) is the approximate date when a pregnancy is expected to reach full term (around 40 weeks from the start of the last menstrual period). It's a helpful reference point for tracking pregnancy progress and planning prenatal care.

Common Calculation Methods

The most common way to calculate a due date is:

• Last Menstrual Period (LMP) method: Count 280 days (40 weeks) from the first day of the last menstrual period. This is the standard method used by many healthcare providers.
• Conception date method: If you know the conception date, add 38 weeks (266 days) to that date, or subtract 14 days from the conception date to estimate LMP, then add 280 days.
• IVF transfer date method: For pregnancies from IVF, the gestational age at transfer is known, so the due date is calculated by working backwards from the transfer date to estimate LMP, then adding 280 days.
• Ultrasound dating: Healthcare providers often use early ultrasound measurements (especially in the first trimester) to refine or adjust the due date, as this can be more accurate than LMP-based calculations for some pregnancies.

This calculator uses simple calendar math based on the dates you enter. It does not perform ultrasound measurements or account for individual variations in pregnancy length.

It's important to understand that due dates are estimates, not exact predictions. Only about 5% of babies are born exactly on their due date. Most babies arrive within a window of about two weeks before or two weeks after the due date.

Factors That Affect Timing

• Individual variation: Every pregnancy is unique. Some babies develop faster or slower than average.
• Cycle length: If your menstrual cycle is longer or shorter than 28 days, LMP-based calculations may be less accurate.
• Uncertainty about dates: If you're not sure of your LMP or conception date, the estimate may be less accurate.
• Multiple pregnancies: Twins, triplets, and other multiple pregnancies often have different due dates and may deliver earlier than singleton pregnancies.
• Medical factors: Some medical conditions or complications may affect pregnancy length.

For these reasons, healthcare providers often use early ultrasound to refine due dates, and they may adjust the due date based on clinical findings throughout pregnancy.

Pregnancy is typically counted in weeks from the first day of the last menstrual period (LMP), even though conception usually occurs about two weeks later. This is a standard convention used by healthcare providers worldwide.

Trimesters

Pregnancy is divided into three trimesters:

• First trimester: Weeks 0-12. Early development, many changes happening rapidly.
• Second trimester: Weeks 13-27. Often called the "honeymoon period" of pregnancy, when many people feel their best.
• Third trimester: Weeks 28-40. Final growth and preparation for birth.

These divisions are helpful for understanding pregnancy progress and when certain tests, screenings, and milestones typically occur. However, individual experiences can vary significantly.

While LMP-based calculations are a good starting point, healthcare providers often use ultrasound to refine due dates, especially early in pregnancy.

Why Ultrasound Is More Accurate

• Early measurements: In the first trimester, fetal size is very consistent, so ultrasound measurements can provide a more accurate estimate of gestational age than LMP alone.
• Accounts for cycle variation: Ultrasound doesn't depend on knowing your exact LMP or cycle length.
• Confirms viability: Early ultrasounds can confirm that the pregnancy is developing as expected.
• Multiple pregnancy detection: Ultrasound can identify multiple pregnancies, which may have different due dates.

Why Clinician Guidance Matters

Your healthcare provider considers many factors when determining your due date, including:

• Your medical history
• Ultrasound measurements
• Physical examination findings
• Any complications or risk factors
• Your individual circumstances

For these reasons, your healthcare provider's due date should always take priority over calculator estimates. This tool is for educational awareness only.

This calculator provides simple calendar-based estimates. It cannot diagnose, treat, or provide medical advice about your pregnancy.

When to Contact Your Healthcare Provider

You should contact your healthcare provider or seek immediate medical attention if you experience:

• Severe abdominal pain or cramping
• Heavy bleeding or unusual discharge
• Signs of preterm labor (regular contractions before 37 weeks)
• Decreased fetal movement (in later pregnancy)
• Severe headaches, vision changes, or other concerning symptoms
• Any other symptoms that worry you