Calculator: Pregnancy Weeks – What Happens Right Now in my Belly?

Curious about how far along you are? Do you have an idea which trimester you are currently in? This guide will provide you with essential information on each phase of your pregnancy, may it be weekly or per trimester. All you have to do is to enter the day of your last period and the length of your menstrual cycle. Then, the pregnancy weeks calendar will present you all the relevant information that you need.
At a Glance
  • There is no absolute way of knowing when you actually conceived or ovulated. Because of this, most people determine the date of pregnancy based on the LMP or the last menstrual period.
  • Because there is no accurate way to determine the date of conception, most healthcare professionals tell you that you are pregnant for about two weeks longer than you really have been.
  • Your stage of pregnancy is measured in pregnancy weeks (PW), and pregnancy typically lasts for 40 pregnancy weeks or 281 days.
  • Your total duration of pregnancy can also be divided into three periods known as trimesters. Every trimester is the equivalent of three months. The first trimester is the date of conception until the 12th week of pregnancy. The second trimester is from the 13th to 27th week of pregnancy. And the third trimester is from the 28th week of pregnancy until the date of birth.
  • The best time to determine your baby’s sex through ultrasound is on your 20th week of pregnancy. This is when the sexual organ has already clearly developed.

Your Pregnancy Weeks

Your stage of pregnancy is measured in pregnancy weeks (PW). Typically, pregnancy lasts for 40 PWs or 281 days [Source: New York State Department of Health]. Taking this into account, the first day of your most recent menstruation is relatively the start of your pregnancy.

Most women are not aware of their exact date of conception. For this reason, the simplest way to calculate it is by determining the first day of the most recent menstruation. But medically speaking, ovulation or the time when an egg is fertilized occurs about 14 to 16 days after the start of the menstruation period.

Because we measure your pregnancy from the beginning of your last period, your baby is actually two weeks younger than your pregnancy start date. This is called your baby’s gestational age. So when your doctor tells you that you are five weeks pregnant, your baby’s gestational age is actually three weeks.

Pregnancy Weeks Calculator

How do you calculate your Pregnancy Week (PW)?

Example: 12th week of pregnancy means that 11 weeks plus 1 to 7 days of pregnancy have already elapsed.

11W3 = 11 completed weeks of pregnancy + 3 days = pregnancy weeks + 3 days = 12th PW

Division of Pregnancy Into 3 Trimesters

Trimester means three months. 

  • The date of conception until “week 12” of your pregnancy is your first trimester.
  • Your second trimester is from “week 13” to “week 27”.
  • Lastly, the third trimester lasts from “week 28” until the date of birth.

What Happens During Each Trimester

Each trimester is different. They come with their own specific changes – both hormonal and physiological. These changes will not be easy on you. So what can you do to ride out these trimesters with as very little stress as possible? By being aware of the ways your baby is growing and affecting your body, you can prepare yourself better. Educating yourself about the progress of your pregnancy can also help in avoiding certain risks and factors that can happen during each trimester.

1st Trimester

Although the same duration as other trimesters, a lot of women feel like first trimesters are much sorter. It is probably because most women are not aware that they are pregnant during the first month. First trimesters last from conception until the 12th week of pregnancy. Although your physical appearance doesn’t change much at this stage, a lot of things are happening to your body in preparation for the months to come.

Your hormone levels change in significant ways. Your uterus prepares to carry your baby, blood supply is added to it to nourish the growling life and your heart rate increases. This is when most of the symptoms of pregnancy show up – morning sickness, general fatigue, headaches, constipation and many others.

It is best to start taking folic acid during this stage. The 1st trimester is when the fetus develops all of its vital organs. Having a healthy diet that includes folic acid helps prevent neural tube defects. Additionally, avoid smoking, drinking alcohol or any form of drug use to prevent serious pregnancy complications and childbirth defects.

2nd Trimester

Often called “The Magic Middle”, second trimester (13 – 27 weeks) is usually a relatively mild period of pregnancy. During this period, women often take a break from all the fatigue, nausea and many other pregnancy symptoms. You will also most likely experience an energy spurt during the day and be able to sleep relatively well during the night. Most women find this the most comfortable time of pregnancy.

Your abdomen will start looking pregnant as this is when the uterus grows rapidly in size. Certain changes you may experience include; a stronger appetite, weight gain, and body pains like leg cramps, nasal congestion, and backaches. Your baby will also start making movement inside of you during the second trimester. They may even be able to hear and recognize your voice.

It is best to start investing on comfortable maternity clothing at this point. This is when your belly starts to grow rapidly and your clothes will no longer fit you. Check out our article on maternity clothes for more information.

3rd Trimester

The third trimester  (28 weeks to date of birth) is when you will start looking obviously pregnant. This is the most uncomfortable stage of pregnancy. You will experience all sorts of discomfort from swelling of the feet to even worse backaches. Mobility at this point is also restricted. Since you are nearing labor, you will be visiting your doctor more frequently. This is when you are regularly tested for protein and checked for blood pressure and fetal heart rate. Your doctor will also start checking your cervix to determine your baby’s position. All of this is in preparation for childbirth.

You should start considering your childbirth options from here. This is the best time to start taking childbirth classes to help you and your partner prepare for the arrival of your expected date of delivery. Remember, preparedness is key.

Pregnant woman at doctor checks pregnancy week

Determining a baby’s gender or sex

One of the most exciting parts of pregnancy is anticipating and knowing the sex of the baby before birth. However, during the first week of pregnancy, the embryo looks the same under an ultrasound. This makes the process more puzzling.

At this phase of pregnancy, the embryo displays a bulge or a bud, known as protuberance. For female offspring, their body starts to produce female hormones beginning at the 8th week of pregnancy. As gestation continues, this bud develops into a penis or a vagina. But since the formation of the sex organ is a slow process, only during the 12th week of pregnancy are we able to identify the baby’s sex organ [Source: Women’s Health]. Even then, determining the sex or gender of the baby at this phase under an ultrasound can still be challenging for most sonography specialists. In fact, statistics show that there is only 68% success rate. Other reasons include the following:

  • The baby is lying incorrectly and rolled up
  • The baby is moving during the ultrasound
  • The sexual organ of the baby has only developed slightly
Pro Tip: The best time to determine your baby’s sex through ultrasound is on your 20th week of pregnancy. This is when the sexual organ has already clearly developed.


Pregnancy is a unique time in your life. You will never experience anything quite like it. It imposes such changes in your whole being that it is important, now more than ever, to have a good support system. Make sure you are surrounded by people who will not only give you physical support but emotional as well. It is also very important to visit your doctor frequently. This is so you can monitor your pregnancy for the best possible outcome. By having a great support system and taking all prenatal tests and check-ups – you are giving your baby a healthy headstart in life.

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