Pregnancy due date calculator

Select a method for calculating your due date

Last period Conception date Ultrasound Due date

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When was your last period?

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Whats your regular cycle length?

Cycle length I don't know 20 days 21 days 22 days 23 days 24 days 25 days 26 days 27 days 28 days 29 days 30 days 31 days 32 days 33 days 34 days 35 days 36 days 37 days 38 days 39 days 40 days 41 days 42 days 43 days 44 days 45 days Since cycles vary, we’ll use a standard 28-day average for your calculation.

When did conception occur?

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Date of ultrasound

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Gestational age at ultrasound

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Days 0 1 2 3 4 5 6

Your estimated due date

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How to find out the estimated due date?

Your due date (EDD) can be estimated in several ways. Each of them relies on slightly different data, so the results may differ depending on the method you choose.

Important to know:

• Only 4 to 5 percent of babies are born exactly on the estimated due date.
• Full-term pregnancy normally lasts from 37 to 42 weeks.
• EDD is an estimate that may be adjusted following a medical examination.
• Results may slightly differ depending on what input data you use — your menstrual cycle, conception date, or ultrasound date.

First Day of the Last Period

This is the most common way to estimate a due date. It is based on the first day of the last period, as this date is usually easier to remember than the exact day of conception.

On average, pregnancy lasts about 40 weeks (280 days), so the calculation is simple: 280 days are added to the first day of the last menstrual period. This method is known as Naegele’s rule.

Formula: Due date = first day of the last period + 280 days

Another way is to subtract 3 months from the date of the last period and add 7 days.

For example, the first day of your last menstrual period was January 10.

• Minus 3 months → October 10;
• Plus 7 days → October 17.

Estimated due date: October 17.

This method assumes a regular 28-day cycle and ovulation occurring around day 14 of your cycle. If your menstruation is irregular, the estimated date may be less accurate, but it remains a reliable starting point and is widely used by doctors.

Conception Date

If you know the date of conception, you can estimate the due date by adding 38 weeks (266 days) to that date. This method may seem more accurate, especially if you have been tracking ovulation or planning your pregnancy.

However, determining the exact date of conception is not always possible. Sperm can remain viable in a woman’s body for up to five days, and ovulation does not always occur on the same day of the menstrual cycle. It means that even if you know the day of the intercourse, fertilization could have occurred later.

Therefore, doctors do not use the conception date alone, but it can be a useful benchmark.

Early Ultrasound Scan

Early ultrasound, especially in the first trimester, is considered one of the most accurate methods to estimate a due date. This method is often used to confirm or adjust the EDD calculated based on the period date.

During the examination, the doctor measures the embryo’s size — usually, crown-to-rump. These measurements help determine the gestational age and calculate the EDD more accurately.

This method is especially useful for women with irregular cycles or those unsure of the last period date or conception date. In such cases, ultrasound can be used as the primary method for estimating your gestational age.

According to The American College of Obstetricians and Gynecologists, the first-trimester ultrasound is the most accurate method to establish the gestational age and due date.

How Far Along Am I?

If you already know your estimated due date, determining your current gestational age is easy. The calculator counts back from your EDD (40 weeks of pregnancy) to the present day and displays your gestational age in weeks and days.

Pregnancy is usually split into three trimesters:

As the due date approaches, you can also come across the following terms:

• Premature birth: before 37 weeks;
• Early term: between 37 weeks, 0 days and 38 weeks, 6 days;
• Full term: between 39 weeks, 0 days and 40 weeks, 6 days;
• Late term: between 41 weeks, 0 days and 41 weeks, 6 days;
• Postterm: 42 weeks and more.

These categories help medical professionals evaluate gestation course, and make decisions about the safest delivery options for both the mother and the baby.