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How does a due date calculator work?

How does a due date calculator work?

Are you wondering how many weeks pregnant you might be? And if you are pregnant, do you want to know how on earth medical doctors calculate your due date? 

It’s a lot to take in and we understand. If you’re feeling overwhelmed, we’re here to give you the information you need to answer these looming questions. In fact, these are all very normal questions to have — and these questions deserve genuine answers to help you make informed choices about your health. And that’s what we are here to do for you at ThriVe+.

Thoughtful African American lady wondering how to use a due date calculator.

Let’s take the mystery out of the due date calculator. Medical professionals use a due date calculator to determine your estimated pregnancy due date, and therefore how far along you are in your pregnancy. When you visit a medical provider, they will ask for some information regarding your menstrual cycle. Then they will do a little math (that we will walk you through!) If you are unable to see a medical provider right away, there are online due date calculators available.1

Here are two commonly used methods to calculate the due date. Both methods begin with the first day of your last menstrual period (LMP). For the first method, the medical provider starts with the first day of your LMP and adds seven days to that date. Then, they will count back three months from that date to arrive at the estimated due date. For the second method, the medical provider uses the first day of your LMP and counts 40 weeks forward from there. Both methods calculate your pregnancy to last 40 weeks.2 This is the due date calculator in a nutshell. Not too intimidating, right? However, it is not uncommon for deliveries to happen a week or even two weeks before or after the estimated due date. If you can’t remember when your LMP began, that’s okay too. Not to worry — an ultrasound provides another way to confirm the length of your pregnancy.3

An ultrasound in the first trimester is important because it confirms how many weeks along you are in your pregnancy. As well as monitoring growth and development of the fetus, an ultrasound can assess the overall health of your pregnancy.3 ThriVe+ offers no-cost ultrasounds to you by licensed medical professionals. ThriVe+’s medical professionals are here to answer your questions and help you along this journey because your questions are important, and you are not alone. We are with you!

Stages to become pregnant (ovulation, fertilization, implantation)

We’ve talked about how a due date calculator works, but let’s talk about what happens when you become pregnant. The stages to become pregnant begin with ovulation, then fertilization, and finally implantation.3 Here is a quick overview. Ovulation occurs around the 14th day of a woman’s menstrual cycle. At that time, the ovary releases an egg into the fallopian tube. The egg is ready to be fertilized.4 Fertilization occurs when the sperm meets the egg and the two become one, now a fertilized egg. This happens when the sperm makes its way to the fallopian tube, or the sperm was previously there. Sperm can live inside a woman’s body for up to five days under the right circumstances.4 The fertilized egg then moves down the fallopian tube into the uterus. It implants along the wall of the uterus to continue the growing and dividing of cells. A process known as implantation.3 If the fertilization process does not occur, your body sheds the lining of the uterus, which results in your period.

Calculations can be off for a number of reasons

The due date calculator is not always 100% accurate. It can be off by a few days for a number of reasons. A woman’s menstrual cycle on average lasts 28 days. However, it’s not uncommon for women to have irregular menstrual cycles that last longer or shorter than 28 days. Ovulation therefore does not always land on the 14th day of a woman’s cycle.4 As mentioned above, if you can’t remember the beginning of your last menstrual period, don’t worry — it’s not a problem. A medical professional will confirm the length of your pregnancy with an ultrasound to determine an accurate estimated due date.

Close-up shot of a young Arab woman, confident about using a due date calculator.

Confirm pregnancy with an ultrasound to be sure

If you are unsure about your menstrual cycle regularity (or you don’t remember the date of your last menstrual cycle and you think you are pregnant), ThriVe+ is here to help you. We can provide you with the information and medical services you need to determine if you are pregnant and, if so, how far along you are in your pregnancy. 

Ultrasounds are the most accurate way to determine the length and health of your pregnancy.3 ThriVe+ is available to provide you with the information you need to decide what’s best for you — no judgment. We simply offer you the best world-class care at no-cost, so you can freely make informed decisions based on your values. You deserve to be informed and know your options in abortion, adoption, and parenting. We’ll provide you with information on these options with no judgment and emotional support. Ultrasounds are also important because it is a way of confirming a positive pregnancy and the viability of your pregnancy in the very early stages.3 If the due date obtained from the due date calculator differs from the date obtained from the ultrasound, medical providers will likely use the ultrasound date as the official due date. 

ThriVe+ offers pregnancy tests

If you think you are pregnant, and you want to know for sure, please contact ThriVe+. We are happy to offer a lab-quality pregnancy test performed by one of our medical professionals at no-cost to you. Results of your pregnancy test are trustworthy and provided to you during your appointment.






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