Due Date Calculator

Table of contents:
This calculator, which is also known as a pregnancy calculator, estimates your due date. While your baby is going to make its own decision, it’s helpful if you can figure out the date as well. Below, you can read about the calculator itself, calculation methods, and information on pregnancy in general.

What is a Pregnancy Due Date?

For many people, pregnancy is one of the most exciting parts of life. It’s the celebration of two people creating a beautiful new person. After conception, the baby usually stays in the womb for 280 days, equal to nine months. This period covers the final menstrual period through until birth. 

While it’s true that not every baby is going to follow your schedule or estimations, it’s helpful to have them. Using a due date calculator can offer time to plan, add dates to maternity leave, and get the baby’s room ready.

The Estimated Due Date

You use an estimated due date, or EDD, to predict when labor will occur. Many things contribute to the date, which is why it’s an estimate. No one can predict the exact day of birth. Only around four percent of babies decide to turn up on the estimated date.

What is a Due Month?

Around 80 percent of babies are born within two weeks of their EDD. The inaccuracy of the due date means that most people set their due month. Having a due month allows expectations that a baby will be born in a fixed month. Most babies are born from 37 to 42 weeks, so you can use the due date calculator to work out your due month. Find this information in the advanced mode section, using a two-week window.

Due month = due date -/+ two weeks

How Do You Calculate A Baby’s Due Date?

Believe it or not, there are scientifically proven pregnancy due date calculations. Some are simple, some not so much. They might be scientific, but that still doesn’t mean the baby is going to follow your rules. Don’t take the due date calculator’s predictions as gospel. 

As your pregnancy progresses, some doctors may even change that due date. Irregular periods, growth, and abnormal protein levels can alter their estimate. Use the following methods to determine your due date. 

1.	Naegele’s Rule – the first day of your last menstrual cycle 
2.	The day you conceived 
3.	Pregnancy milestones 
4.	Fundal height 
5.	The Mittendorf-Williams Rule 
6.	Doppler ultrasonography

This due date calculator uses the date of conception and Naegele’s Rule.

What is LMP?

LMP is the abbreviation for last menstrual period. Medical professionals date your pregnancy from the first day of your final period. LMP will refer to the onset of bleeding on that first day before you become pregnant. If you use this form of calculation, you are six weeks pregnant two weeks after you miss your period.

What is Naegele’s Rule?

Naegele’s Rule is the first day of the LMP method. It adds 280 days, or 40 weeks, to the first day of your last period. The formula looks like this:

Due date = first day of last period + 280 days

The LMP method considers a standard 28-day cycle. Conception follows after two weeks. The accuracy of Naegele depends on your cycle length and your LMP recall ability. Some women also experience light bleeding when they are in the early stages of pregnancy. They take this to be their period when they could be pregnant for a few weeks beforehand. 

As most women know, periods aren’t precisely four weeks apart. If you have a longer cycle, you could conceive your baby later. If it’s short, conception could be early.

What is a Conception Date?

The date of conception is the day fertilization occurs. A sperm connects with an egg, and the zygote grows and divides to form a new organism. It can be tricky for those who don’t track ovulation to know their conception date. If you have a regular menstrual cycle, you can assume that conception is two weeks after LMP.

Sperm can live inside a vagina for five days, with eggs up to 24 hours. There is a six-day window for pregnancy to occur.

The Conception Date Method

If you know your conception date, use the second calculation method in the calculator. The due date calculator will add 38 weeks, or 266 days, to your entered date. With this method, you get a more reliable result than LMP. The formula for this method is: 

Due date = date of conception + 266 days

How to Calculate Your Baby’s Due Date

If you can’t wait to know when your baby will be born, then read on. Our due date and pregnancy calculator can offer an estimation in four steps. 

1.	Choose your method – LMP or conception date 
2.	Enter the dates 
3.	Set your average cycle 
4.	Read the result for your due date and pregnancy progress! 

Advanced Mode
You can use the due date calculator for advanced information as well. Find out your due month’s time span, pregnancy percentage completion, and how days until your baby’s birth.

When is My Baby’s Due Date?

Let’s take a look at how pregnancy calculations work. Follow this example below to be 100 percent certain! 

You’re pregnant, and want to work out your due date with different methods. 

Using the LMP method
Your last period was on March 10, 2019. Your average cycle is 30 days. 

March 10, 2019 + 280 days + 2 = December 17, 2019

Your due month

Start of due month = December, 17, 2019 – 14 days = December 3, 2019
End of due month = December 17, 2019 + 14 days = December 31, 2019

The conception day method
What if you knew the day you conceived? Let’s say you conceived on March 10, 2019. 

March 10, 2019 + 266 days = December 1, 2019

The due month would then be:

Beginning of due month = December 1, 2019 – 14 days = November 18, 2019
End of due month = December 1, 2019 + 14 days = December 15, 2019

How Long is a Pregnancy?

Most pregnancies are 37 to 42 weeks long. There is also a five-week window that allows for a healthy baby born to term. A baby born before the 37-week mark is premature and may need medical care. If a baby is born after 42 weeks, there may be a higher chance of complications. 

If the mother is carrying multiple babies, premature birth is common. The more babies, the earlier they are born. The embryo implant timeframe can also determine the pregnancy length. Tall women often have longer pregnancies than short women. If you are a white European, your pregnancy may also be longer than an Asian woman.

What is a Pregnancy Trimester?

A pregnancy trimester is a stage of pregnancy. There are three in every pregnancy, split into three-month periods. The first trimester is from one to 12 weeks, including conception. Risks of miscarriage are high during this trimester. 

During the first trimester, your entire body changes – along with your hormones. Having your period stop is often a clear sign of pregnancy. You may also experience mood swings, tender breasts, and weight gain or loss. Constipation, fatigue, headaches, and frequent urination are common as well.

The first trimester is also when your baby’s heart, lungs, arms, legs, spinal cord, brain, and nerves begin to form. Nausea and fatigue can often kick in during the second trimester. This one occurs from week 13 to 28.  Your stomach starts to grow, you feel baby movements, and your body may ache and stretch. In your second trimester, your baby will grow to around five inches long. It can now swallow, hear, and bend its arms and legs. 

From week 29 to birth is the third trimester. You will experience many discomforts of the first two, as well as frequent bathroom trips. Breathing difficulties, tender breasts, and sleeping trouble might occur too. Toward the end, you can start contractions which can be real or false labor. 

Once you reach your due date, your cervix softens and thins out. The baby then starts moving toward the birth canal, ready to show up in the world.

Causes of Premature Birth

Premature birth of babies can occur for many reasons, including these below: 

    	Previous premature births
    	A small interval between pregnancies
    	Multiple pregnancies
    	In vitro fertilization
    	Genital or other infections
    	Chronic disorders
    	Cigarette smoking 
    	Injury or trauma
    	Overweight or underweight
    	Miscarriages and abortions

This graph shows median birth weights, lengths, and head circumferences for premature babies.


Gestational age Weight
Head circumference
40 weeks 7 / 3.6 20 / 51 13.8 / 35
35 weeks 5 / 2.5 18.1 / 46 12.6 / 32
32 weeks 3 / 1.8 16.5 / 42 11.6 / 29.5
28 weeks 2 / 1.1 14.4 / 36.5 10.2 / 26
24 weeks 1 / 0.65 12.2 / 31 8.7 / 22
For girls:
Gestational age Weight
Head circumference
40 weeks 7 / 3.4 20 / 51 13.8 / 35
35 weeks 5 / 2.4 17.7 / 45 12.4 / 31.5
32 weeks 3 / 1.7 16,5 / 42 11.4 / 29
28 weeks 2 / 1.0 14.1 / 36 9.8 / 25
24 weeks 1 / 0.60 12.6 / 32 8.3 / 21

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