Week by week pregnancy based on due date

Some women's cycles are not exactly 28 days. Adjust the cycle length if your cycle is shorter or longer than 28 days.

Table of Contents Show

Using the due date calculator
Track your pregnancy
How can I calculate important week-by-week information throughout my pregnancy?
To create a Week-By-Week calendar choose from the following options:
What is my due date based on weeks pregnant?
How do you calculate what week of pregnancy?
When did I conceive based on due date?
When did I conceive and how many weeks am I?

Using the due date calculator

To find your due date, enter the date of the first day of your last period, and select 'show your due date'. Pregnancy normally lasts from 37 weeks to 42 weeks from the first day of your last period.

You need to know the first day of your last period to use this calculator. If you do not know it or are unsure, speak to a midwife or GP.

As part of your pregnancy (antenatal) care, your midwife will offer you a 12-week scan that may give you a more accurate date for the birth of your baby.

Find out about:

your NHS pregnancy journey
your first midwife appointment
health things you should know when you're pregnant

Find out about what's happening when you're:

1, 2 or 3 weeks pregnant
4 weeks pregnant
5 weeks pregnant
6 weeks pregnant
7 weeks pregnant
8 weeks pregnant

While it’s true that most pregnancies last 40 weeks, there are other factors at play which will determine your due date. Most expectant mothers don’t realize that both menstrual and ovulation periods count as the first two weeks of pregnancy. Many won’t be aware of their pregnancy until their first missed period, and by that time they could be up to five weeks in. That means that simply estimating nine months from the day you take a pregnancy test isn’t going to calculate your due date, and, even so, factoring in a few weeks here and there for ovulation won’t either.

Unless you can pinpoint exactly what point of your ovulation cycle you were in at the time of fertilization, it’s difficult to know how far along you are and what date you’ll meet your baby. Luckily, our Due Date Calculator can help.

Using both the date of your last period and the length of your regular cycle, or exact date of conception, our Due Date Calculator will quickly work out your estimated due date, tailoring it accordingly for longer, shorter, and average cycle lengths.

How far along you are determines nearly everything in your pregnancy including blood tests, ultrasound examinations, and more importantly when you can expect your baby to be born. It also helps you identify certain situations to learn what is normal and when to have procedures done. What is normal at 26 weeks may not be normal at 32 weeks. Also, tests that should be done at 20 weeks but are done at 16 weeks could be interpreted incorrectly.

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How can I calculate important week-by-week information throughout my pregnancy?

This pregnancy calculator helps you find out exactly how many weeks pregnant you are right now, details your baby's development, and precisely what is happening to your body at the moment. Just enter your pregnancy due date or other information to create and calculate a personalized weekly and daily pregnancy calendar. The babyMed Monthly Pregnancy Calculator and Calendar is a week-by-week pregnancy calculator and calendar with information for each day of your pregnancy.

To create a Week-By-Week calendar choose from the following options:

Weekly Count: Follow new developments in weeks and days
Daily Countup: Count up how many days you are into your pregnancy
Daily Countdown: Count down your days left until your due date
Fetal Weight: Available in ounces or grams
Ultrasound measurements: BPD, FL, HC, AC

The chart below provides links to detailed information about what happens each week during pregnancy.

1st Trimester2nd Trimester3rd Trimester1 wk pregnant14 wks pregnant27 wks pregnant2 wks pregnant15 wks pregnant28 wks pregnant3 wks pregnant16 wks pregnant29 wks pregnant4 wks pregnant17 wks pregnant30 wks pregnant 5 wks pregnant18 wks pregnant31 wks pregnant 6 wks pregnant19 wks pregnant32 wks pregnant 7 wks pregnant20 wks pregnant33 wks pregnant 8 wks pregnant21 wks pregnant34 wks pregnant 9 wks pregnant22 wks pregnant35 wks pregnant 10 wks pregnant23 wks pregnant36 wks pregnant 11 wks pregnant24 wks pregnant 37 wks pregnant 12 wks pregnant25 wks pregnant 38 wks pregnant 13 wks pregnant 26 wks pregnant39 wks pregnant 40 wks pregnant 41+ wks pregnant

Don't know your due date? Use our Pregnancy Calculator to find out the exact due date, with dates for exciting pregnancy events.

What is my due date based on weeks pregnant?

Most pregnancies last around 40 weeks (or 38 weeks from conception), so typically the best way to estimate your due date is to count 40 weeks, or 280 days, from the first day of your last menstrual period (LMP). You could also subtract three months from the first day of your last period and add seven days.

How do you calculate what week of pregnancy?

To determine how many weeks pregnant you are, count how many weeks it has been since the first day of your LMP. For example, if your last period started on April 3 and it is now May 22, then you are 7 weeks pregnant.

When did I conceive based on due date?

For a regular 28-day cycle, pregnancy is estimated to be 280 days, or 40 weeks, from your last menstrual period, and 266 days, or 38 weeks, from the date of ovulation. Therefore, to calculate the most likely date of conception, you need to subtract 266 days from your estimated due date.

When did I conceive and how many weeks am I?

To estimate your conception date based on your menstrual cycle, simply add approximately two weeks from the first day of the last menstrual period you had before you became pregnant. This should give you the start of your ovulation period, when your body is most fertile and likely to become pregnant.