Pregnancy Due Date Calculator Based on Last Period

Pregnancy Trimester Calculator by Week

Track your pregnancy journey week by week and visualize your progress through each trimester.

Our Pregnancy Trimester Calculator helps you track your pregnancy progress, determine your current trimester, and visualize your journey to motherhood. Simply enter your last menstrual period date or conception date to get personalized insights about your pregnancy timeline.

Enter Your Pregnancy Information

Last Menstrual Period

Conception Date

Date: ? Select the first day of your last menstrual period or your estimated conception date.

Your Pregnancy Timeline

Current Pregnancy Week

-

Current Trimester

-

Estimated Due Date

-

Days Until Due Date

-

0%

Complete

Weekly Milestone

-

Disclaimer: This pregnancy calculator provides estimates based on the information you provide. It is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding your pregnancy.

Understanding Pregnancy Trimesters

Pregnancy is typically divided into three trimesters, each lasting approximately three months. Understanding these trimesters can help you track your baby's development and anticipate the changes in your body throughout your pregnancy journey.

First Trimester (Weeks 1-13)

The first trimester begins on the first day of your last menstrual period and lasts until the end of week 13. During this time, your body undergoes significant hormonal changes as it prepares to nurture a growing fetus. Many women experience symptoms like morning sickness, fatigue, and breast tenderness during this trimester.

Despite being early in the pregnancy, incredible development is happening. By the end of the first trimester, your baby will have developed all major organs and body systems, though they are still immature. The baby is about the size of a lemon by week 13.

Second Trimester (Weeks 14-27)

The second trimester is often called the "golden period" of pregnancy because many women find their early pregnancy symptoms subsiding while they haven't yet developed the discomforts of the third trimester. During this time, you'll likely begin to feel your baby move, and your belly will become noticeably rounded.

Your baby continues to develop rapidly during the second trimester. By around week 20, you may be able to learn your baby's sex if you choose. The baby's senses develop, and they can hear sounds from the outside world. By the end of this trimester, your baby is about the size of a cauliflower and has a chance of survival if born prematurely, though they would require intensive medical care.

Third Trimester (Weeks 28-40)

The third trimester spans from week 28 until the birth of your baby. During this time, your baby grows significantly in size and weight. You may experience increased discomfort as your expanding uterus puts pressure on your organs and causes back pain, heartburn, and difficulty sleeping.

In the third trimester, your baby's lungs mature, and they practice breathing movements. They develop more body fat, and their brain continues to grow rapidly. By week 37, your baby is considered full-term and could arrive at any time. Most babies are born between weeks 38 and 42 of pregnancy.

How Pregnancy Dating Works

Pregnancy is typically calculated as 40 weeks (280 days) from the first day of your last menstrual period (LMP), even though conception usually occurs about two weeks after this date. This method is used because most women know when their last period began but may not know exactly when conception occurred.

If you know your conception date (the date when the egg was fertilized), your healthcare provider may calculate your due date as 266 days (38 weeks) from that date. Both methods should yield approximately the same due date.

Tracking Your Pregnancy Progress

Throughout your pregnancy, your healthcare provider will monitor your progress through regular prenatal visits. These visits typically include measurements of your belly, checking your blood pressure and weight, and listening to your baby's heartbeat. You may also have ultrasound scans to check on your baby's growth and development.

Using a pregnancy calculator like this one can help you understand where you are in your pregnancy journey and what to expect in the coming weeks. However, remember that every pregnancy is unique, and your experience may differ from the general patterns described here.

Frequently Asked Questions

How accurate is the pregnancy due date calculator? ▼

Pregnancy due date calculators provide an estimate based on the first day of your last menstrual period. While this method is standard, only about 5% of babies are born on their exact due date. Most babies arrive between 38 and 42 weeks of pregnancy. Your healthcare provider may adjust your due date based on ultrasound measurements taken in the first trimester, which can be more accurate than dating based on your last menstrual period.

What if I don't know the date of my last menstrual period? ▼

If you don't know the date of your last menstrual period, your healthcare provider can estimate your due date using an early ultrasound. In the first trimester, ultrasound measurements of the fetus are very accurate for determining gestational age. Later in pregnancy, ultrasound becomes less accurate for dating because babies grow at different rates. If you have irregular periods or don't track your menstrual cycle, an early ultrasound is the best way to establish your due date.

Can my due date change during pregnancy? ▼

Yes, your due date can change during pregnancy, especially if it was initially calculated based on your last menstrual period. If an early ultrasound shows a significant discrepancy (more than 5-7 days) between your menstrual dating and the ultrasound measurements, your healthcare provider may adjust your due date. After the first trimester, due dates are rarely changed unless there's a substantial difference, as fetal growth becomes more variable.

What is the difference between gestational age and fetal age? ▼

Gestational age is the age of the pregnancy calculated from the first day of your last menstrual period, which is typically two weeks before conception occurred. Fetal age is the actual age of the fetus from the date of conception. Healthcare providers typically use gestational age when discussing pregnancy progress, which is why a full-term pregnancy is considered 40 weeks (gestational age) even though the fetus has only been developing for about 38 weeks (fetal age). Our calculator uses gestational age, which is the standard medical approach.

How do I know which trimester I'm in? ▼

Pregnancy is divided into three trimesters: - First trimester: Week 1 to the end of week 13 - Second trimester: Week 14 to the end of week 27 - Third trimester: Week 28 until birth Our calculator automatically determines which trimester you're in based on the due date calculated from your last menstrual period or conception date. Each trimester is associated with different developmental milestones for your baby and different changes in your body.

Is it normal to go past my due date? ▼

Yes, it's common to go past your due date. Only about 5% of babies are born on their exact due date, and about half of pregnancies extend beyond 40 weeks. If your pregnancy continues beyond 41 weeks, your healthcare provider will monitor you and your baby more closely. If you reach 42 weeks (post-term pregnancy), your provider may recommend inducing labor to reduce potential risks. Every pregnancy is different, and your healthcare provider will guide you on the best approach for your situation.

Related calculators