🤰Due Date Calculator

A pregnancy due date calculator gives you an estimated due date (EDD) based on your last menstrual period or conception date. Knowing your due date is the foundation of prenatal care. It determines when you schedule your first appointments, when key screenings take place, and how your healthcare provider monitors your baby's development across all 40 weeks of pregnancy.

Due Date Calculator from Last Period: How Naegele's Rule Works

The most widely used method for calculating your due date is Naegele's rule, named after the 19th-century obstetrician who popularized it. The formula adds 280 days (40 weeks) to the first day of your last menstrual period (LMP). This method is used by obstetricians worldwide and is the basis for the estimated due date on virtually every prenatal chart.

Counting from your last period rather than from conception may seem counterintuitive, but LMP is used because it is a concrete, known date that can be reliably reported. The actual date of conception is rarely known precisely. By convention, the first day of your LMP is defined as the start of Week 0 of pregnancy, even though fertilization has not yet occurred at that point.

This calculator also adjusts for cycle length. Naegele's rule assumes a standard 28-day cycle. If your cycle is longer or shorter, ovulation and conception occur at a different point relative to your LMP, and the due date shifts accordingly.

How to Calculate Pregnancy Due Date: Step by Step

To manually calculate your estimated due date using Naegele's rule, take the first day of your last menstrual period, add one year, subtract three months, and add seven days. For example, if your LMP started on April 1, your estimated due date is January 8 of the following year. Using this calculator is faster and automatically adjusts for your cycle length, which the manual method does not.

The standard pregnancy is 280 days from LMP, but only about 4 to 5% of babies are born on their exact estimated due date. Normal full-term delivery occurs between 37 and 42 weeks of gestational age. The EDD is a statistical midpoint, not an expiration date.

Due Date Calculator by Conception Date

If you know your conception date, such as through IVF, tracked ovulation, or a known single encounter, you can calculate your due date by adding 266 days (38 weeks) to the conception date. Since conception typically occurs 14 days after the LMP in a standard 28-day cycle, the result is usually close to but not always identical to the LMP-based calculation.

If your conception date and LMP date produce different EDDs, an early ultrasound is the most reliable way to resolve the discrepancy. A first-trimester ultrasound can date a pregnancy to within 5 to 7 days, making it more accurate than either date-based method when the two differ.

How Many Weeks Pregnant Am I?

Gestational age, which is what "weeks pregnant" means, is counted from the first day of your LMP. This means you are considered 2 weeks pregnant at the moment of conception, and pregnancy is measured in 40 total weeks from LMP to the estimated due date.

Gestational age differs from fetal age (also called embryonic age). Fetal age counts from conception and is roughly 2 weeks less than gestational age. When your provider says you are 12 weeks pregnant, they mean 12 weeks of gestational age from your LMP, which corresponds to about 10 weeks of fetal development.

The three trimesters divide the 40-week pregnancy as follows: the first trimester covers weeks 1 through 13, the second trimester spans weeks 14 through 27, and the third trimester runs from week 28 through delivery.

Pregnancy Milestones by Trimester

First Trimester: Weeks 1 to 13

The first trimester is the most critical period for fetal development. All major organ systems form between weeks 3 and 8. By week 10, the embryo is officially called a fetus. Miscarriage risk is highest in the first trimester, with approximately 80% of all miscarriages occurring before 12 weeks. Common symptoms include nausea, fatigue, and breast tenderness. Your first prenatal appointment is typically scheduled around weeks 8 to 10.

Second Trimester: Weeks 14 to 27

Most expectant parents find the second trimester the most comfortable phase. Nausea often resolves, energy returns, and the pregnancy becomes visibly apparent. Fetal movement (called quickening) is typically felt for the first time between weeks 16 and 20. The anatomy scan ultrasound around weeks 18 to 20 checks fetal development in detail and can often reveal the baby's sex.

Third Trimester: Weeks 28 to 40

The third trimester is marked by rapid fetal growth and final organ maturation. The fetus gains roughly half of its birth weight during these final weeks. Braxton Hicks contractions become more common. At 37 weeks, a baby is considered full term. Delivery is most common between weeks 39 and 41.

When to Schedule Your First Prenatal Appointment

Most healthcare providers recommend scheduling your first prenatal appointment between 8 and 10 weeks of pregnancy. At this visit, your provider will confirm the pregnancy, review your health history, estimate your due date, and order initial blood tests and possibly a first-trimester ultrasound. If you have a chronic condition, have had a previous pregnancy complication, or are over 35, your provider may want to see you earlier.