Pregnancy Due Date Calculator
Calculate your estimated due date based on your last menstrual period, conception date, or ultrasound. Track your pregnancy progress.
Uses Naegele's rule: LMP + 280 days
Enter your information to calculate your due date.
How It Works
This calculator uses standard obstetric methods to estimate your due date. The most common method is Naegele's rule, which adds 280 days (40 weeks) to the first day of your last menstrual period (LMP). Pregnancy is counted from the LMP, not conception.
If you know your conception date (common with IVF or ovulation tracking), we add 266 days (38 weeks). The ultrasound method back-calculates from the gestational age measured at your scan—often the most accurate method in early pregnancy.
Remember that a due date is an estimate. Only about 5% of babies arrive exactly on their due date. Most babies are born within a window of two weeks before or after the estimated due date (between 38 and 42 weeks).
Frequently Asked Questions
How accurate is the due date?
Due dates are estimates with a range of about 5 weeks (37-42 weeks is considered full term). Early ultrasounds (before 14 weeks) are most accurate for dating. Later measurements have more variation due to different growth rates.
Why is my ultrasound due date different?
Ultrasounds measure the baby's size to estimate gestational age. Early ultrasounds are most accurate because babies grow at similar rates early on. If there's more than a 7-day difference from your LMP date, your provider may adjust your due date.
When do the trimesters start and end?
First trimester: Weeks 1-12. Second trimester: Weeks 13-26. Third trimester: Weeks 27-40. Each trimester brings different development milestones and symptoms.
What is gestational age vs. fetal age?
Gestational age counts from your last period and is the standard used by healthcare providers (40 weeks total). Fetal age counts from conception and is about 2 weeks shorter (38 weeks). This calculator uses gestational age.
What if I don't know my last period date?
If you're unsure of your last period, an early ultrasound (ideally before 14 weeks) is the best way to establish a due date. The earlier the ultrasound, the more accurate the dating. Your provider will help determine the best estimate.