Pregnancy Due Date Calculator

The main thing newly expecting parents want to know is when the baby’s due at the moment of conception. Let our tool help you calculate your baby’s expected birthday! 
    
Your due date is one of the first milestones in pregnancy—the estimated day your baby will arrive. While due dates are just estimates (not guarantees), they serve as an important reference point for prenatal care, fetal development monitoring, and delivery planning. This guide explains how due dates are calculated, how accurate they are, and what factors might shift your due date. Use our calculator above to determine your estimated due date based on your last menstrual period.

What Is a Due Date?

Your due date, also called your estimated date of confinement (EDC) or estimated date of delivery (EDD), is the day your healthcare provider predicts you'll give birth. It's calculated as 280 days (40 weeks) from the first day of your last menstrual period (LMP).

However, "due date" can be misleading because it suggests your baby will arrive on that exact day. In reality, only about 5% of babies are born on their due date. Most babies arrive somewhere within a two-week window: one week before and one week after your calculated due date. This is considered the normal range for full-term pregnancy.

Understanding this helps you stay relaxed as your due date approaches,   if your baby hasn't arrived by the day you expected, you're likely still within the normal range.

How Is Your Due Date Calculated?

Due dates are calculated using Naegele's Rule, a simple mathematical formula used worldwide in obstetrics.

Naegele's Rule Formula

To calculate your due date:

1. Take the first day of your last menstrual period (LMP)
2. Add 280 days (or 40 weeks, or 9 months and 7 days)
3. This gives you your estimated due date

Example:

 If your last menstrual period started on January 1st:

• Add 280 days = approximately October 8th (your due date)

This is exactly what our pregnancy due date calculator does—it performs this calculation instantly based on the LMP date you enter.

When Will You Know Your Due Date?

Your due date is typically established during your first prenatal visit, usually between weeks 8-12 of pregnancy. Your healthcare provider may refine the due date using:

• Ultrasound measurements: An early ultrasound (first trimester) can date a pregnancy very accurately, often within 3-5 days. This is considered the gold standard for dating.
• Last menstrual period: If you have regular cycles, your LMP provides a reliable estimate.
• Physical exam: In rare cases, a clinical exam can help estimate gestational age.

If your ultrasound shows your baby is measuring ahead or behind your LMP-based due date, your healthcare provider may adjust your due date to match the ultrasound findings, as ultrasounds are more accurate early in pregnancy.

How Accurate Is Your Due Date?

While due dates are helpful for planning, they're estimates, not predictions.

Accuracy rates:

• First trimester ultrasound: Accurate within ±3-5 days
• Second trimester ultrasound: Accurate within ±1-2 weeks
• Last menstrual period (with regular cycles): Accurate within ±2 weeks
• Third trimester ultrasound: Accurate within ±2-3 weeks

This means your baby could realistically arrive weeks before or after your due date and still be considered full-term (37+ weeks).

Factors That Affect Your Due Date

Several factors can influence when your baby actually arrives, even if the calculated due date remains the same:

None of these factors guarantee an early or late delivery—they simply increase or decrease the likelihood of variation from your calculated date.

Preparing for Your Due Date

As your due date approaches, use it as a guide for preparing—not an absolute deadline:

Weeks before your due date:

• Install your infant car seat
• Prepare your hospital bag
• Arrange childcare for other children
• Discuss labor and delivery preferences with your healthcare provider
• Take childbirth education classes
• Practice relaxation techniques
• Ensure you have postpartum supplies at home

Around your due date:

• Stay in close contact with your healthcare provider
• Watch for signs of labor (contractions, bleeding, fluid leakage)
• Rest when possible
• Eat nutritious meals
• Stay hydrated
• Continue gentle movement and exercise unless restricted
• Try not to obsess over the exact date

After your due date:

• Don't panic—most babies arrive within 1-2 weeks after the due date
• Your healthcare provider will monitor you closely with stress tests and ultrasounds
• Discuss labor induction options if you go significantly past your due date
• Trust that your body and baby know the right timing