Pregnancy Due Date Calculator

Important Information About Due Dates

Due dates are always estimates. Only a small percentage of people give birth on their exact estimated due date. Most births happen in the few weeks before or after the calculated date.

How estimated due dates are calculated

A common method (often called Naegele’s rule) starts with the first day of the last menstrual period (LMP) and adds 280 days (40 weeks). This assumes ovulation occurs about two weeks after the start of the cycle, which may not be true for everyone.

Why your estimate can change

• Irregular or longer/shorter cycles can shift ovulation timing.
• Uncertainty about the LMP date can reduce accuracy.
• Early ultrasound measurements can refine the estimate.
• Fertility treatments often use known conception dates.

Important limitations

• This calculator is informational and does not replace prenatal care.
• Ultrasound dating in the first trimester is often the most accurate clinical method.
• Always discuss dates, symptoms, and care plans with your healthcare professional.

Sources

• ACOG: Methods for Estimating the Due Date
• Mayo Clinic: Pregnancy due date