Due Date Calculator — When Is My Baby Due? Pregnancy Due Date Estimator

Pregnancy Due Date

Pregnancy lasts about 280 days (40 weeks, or approximately nine months) when counted from the first day of the last menstrual period (LMP). The first symptoms may appear in the first weeks and can then be confirmed with urine or blood pregnancy tests.

Estimated Due Date (EDD)

An Estimated Due Date (EDD) — also called an estimated date of confinement (EDC) or simply a due date — is the most likely date when labor may begin. Many factors influence the length of a pregnancy, so the date is only an estimation. Only about 4% of babies are born exactly on the calculated birth date. It is therefore impossible to define the exact day of childbirth with 100% certainty.

What Is a "Due Month"?

Since so few babies arrive precisely on their predicted due date, the concept of a due month is more realistic. About 80% of babies are born within a window of two weeks before or two weeks after the estimated due date. The formula is simple:

Due month = EDD ± 2 weeks

This four-week window (from 38 to 42 weeks of pregnancy) represents the normal range for a full-term birth.

How to Calculate the Due Date?

There are two main methods for estimating a due date:

1. From the Last Menstrual Period (LMP) — using Naegele's Rule (most common)
2. From the Conception Date — if the date of conception is known

LMP — What Is It?

LMP stands for Last Menstrual Period. It refers to the first day of the last menstrual period before pregnancy. Doctors use this date as the starting point for calculating gestational age and due dates, because it is usually easier to remember than the actual conception date.

It is important to note that the LMP is typically about two weeks before ovulation and conception. This is why gestational age (measured from LMP) is about 2 weeks longer than the actual embryonic age.

Naegele's Rule

Naegele's Rule is the standard obstetric formula for calculating the expected due date. It was described by German obstetrician Franz Karl Naegele in 1812. The rule states:

EDD = LMP + 280 days (for a standard 28-day cycle)

Equivalently: add 1 year, subtract 3 months, and add 7 days to the LMP date.

For cycles other than 28 days, the formula is adjusted:

EDD = LMP + 280 + (cycle length − 28) days

Our calculator automatically applies this adjustment when you enter your cycle length.

What Is a Conception Date?

The conception date is the day the egg was successfully fertilized by a sperm cell. Conception typically occurs around the time of ovulation, which for most women happens approximately 14 days before the next expected period (or cycle length − 14 days from the start of the cycle).

Conception Date Method

If you know (or can estimate) your conception date — for example, from ovulation tracking or fertility treatments — you can calculate the EDD directly:

EDD = Conception Date + 266 days (38 weeks)

Note that 266 days of embryonic development corresponds to 280 days of gestational age (counted from LMP), because the LMP is approximately 14 days before conception.

How Long Is a Pregnancy?

A full-term human pregnancy lasts approximately:

• 280 days from the first day of the LMP
• 266 days from the conception date
• 40 weeks of gestational age
• 38 weeks of embryonic age
• Approximately 9 months and 7 days (from LMP)

Pregnancy Trimesters

Pregnancy is divided into three trimesters:

Premature Birth

A baby born before 37 completed weeks of gestation is considered premature (preterm). Premature babies may require special medical care. The earlier the birth, the greater the potential health challenges:

• Extremely preterm: before 28 weeks
• Very preterm: 28–32 weeks
• Moderate to late preterm: 32–37 weeks

A baby born between 37 and 42 weeks is considered full term. After 42 weeks, the pregnancy is considered post-term.

Gestational Age

Gestational age is the age of the pregnancy measured from the first day of the LMP, expressed in weeks and days. It is the standard medical measurement used to track fetal development and schedule prenatal appointments. Gestational age is always 2 weeks greater than embryonic age (age from conception).

When Should I Schedule the First Medical Examination?

Most doctors and midwives recommend scheduling your first prenatal appointment between 8 and 10 weeks of gestational age. This first visit is important for:

• Confirming the pregnancy and estimating the due date
• Assessing your health and risk factors
• Discussing prenatal vitamins (especially folic acid)
• Ordering initial blood and urine tests
• Possibly performing an early ultrasound

The Tests You Can Expect at the First Doctor Appointment

At your first prenatal visit, your provider will typically perform or order:

• Blood tests: complete blood count (CBC), blood type and Rh factor, rubella immunity, STI screening, thyroid function
• Urine test: protein, glucose, infection screening
• Blood pressure measurement
• Weight and BMI assessment
• Pelvic exam (if indicated)
• Ultrasound: to confirm gestational age and detect multiple pregnancies
• Genetic counseling (if applicable based on age or history)

Frequently Asked Questions (FAQs)

Can I calculate my due date without knowing my LMP?

Yes! If you know your conception date (e.g., from IVF or ovulation tracking), use the Conception Date method in our calculator. Alternatively, an ultrasound in early pregnancy can provide an accurate gestational age estimate.

What if my cycle is longer or shorter than 28 days?

Our calculator adjusts for non-standard cycle lengths. If your cycle is 32 days, for example, the EDD is shifted by 4 days (32 − 28 = 4). Enter your actual average cycle length in the "Cycle Length" field.

How accurate is the due date calculator?

The EDD is an estimate, not a guarantee. Only about 4% of babies are born on their exact due date. About 80% of births occur within ±2 weeks of the EDD (the "due month"). Ultrasound dating in early pregnancy (before 12 weeks) is often more accurate than LMP-based dating alone.

What is the difference between gestational age and fetal age?

Gestational age is counted from the LMP and is what doctors use. Fetal (embryonic) age is counted from conception. The two differ by approximately 2 weeks: gestational age = fetal age + 2 weeks.

When is my baby considered full term?

Full term is defined as 39–40 weeks of gestational age. Babies born at 37–38 weeks are considered "early term," while those born at 41 weeks are "late term," and after 42 weeks, "post-term."