How Many Weeks Pregnant Calculator From Due Date - LMP Due Date Calculator: Free Pregnancy Calculation

Author & Reviewer Dr. Anuja Dokras, MBBS, DNB (Obs & Gynae)
Oxford-trained specialist in Infertility & Women’s Health.
Founder of LMP Calculator.

“Once your doctor gives you your due date, that ‘magic number’ becomes the anchor for your entire pregnancy journey. But every day, you want to know, ‘How many weeks pregnant am I today?’ A calculator that works backward from your due date is the perfect tool for this job. It keeps you updated every step of the way.”

Introduction: Who is This Calculator For?

This calculator is slightly different from a standard pregnancy calculator. A standard calculator uses your LMP (Last Menstrual Period) to estimate your due date.

This “reverse” calculator is for women who already know their Estimated Due Date (EDD) and want to find out exactly how many weeks and days pregnant they are right now.

Part 1: How to Calculate Your Weeks of Pregnancy from Your Due Date

Using this calculator is incredibly simple. You only need one piece of information:

Your Estimated Due Date (EDD): This is the date your doctor gave you, likely based on an ultrasound or your LMP.

Simply enter your due date into the calculator, and it will instantly tell you how many weeks pregnant you are today.

Or if you have a Pregnancy Personal Assistant, you can get your Pregnancy information from here

Part 2: How Does This “Reverse” Calculator Work?

This calculator works on a simple mathematical principle:

Total Pregnancy Duration: A full-term pregnancy is considered to be 40 weeks (or 280 days) long.
Counting Forward from the Past: An easier way to think about it is that the calculator determines the start date of your pregnancy by subtracting 280 days from your due date.
Calculating Elapsed Time: It then calculates the number of days that have passed between that start date and today’s date.
The Result: Finally, the calculator converts those elapsed days into weeks and days to give you your current gestational age.

Example:

Let’s say your due date is December 31st.
The calculator will determine the start of your pregnancy was around March 26th (280 days earlier).
If today is November 1st, it will calculate the number of days between March 26th and November 1st.
That total comes to 220 days.
The calculator converts 220 days into weeks: 31 weeks and 3 days.

You can find out from here how many weeks pregnant you are from the due date

Part 3: Who Should Use This Calculator?

This calculator is particularly useful in these situations:

When Your Due Date Was Set by Ultrasound: If you have irregular periods, a doctor will use a ‘dating scan’ to set your due date. This is more accurate than using your LMP.
For IVF (In Vitro Fertilization) Pregnancies: In IVF pregnancies, the due date is calculated from the date of the embryo transfer, not the LMP.
When You’ve Forgotten Your LMP: If you don’t remember your LMP but your doctor has given you a due date, this calculator is perfect for you.
For Quick Weekly Check-ins: It’s a fast and easy way to track your pregnancy progress week by week.

Expert Opinion – Dr. Anuja Dokras: “For women whose due date is determined by their first-trimester ultrasound, this calculator is the most accurate way to track gestational age. It removes the uncertainties that can come with LMP-based dating.”

Part 4: Understanding Your Results: It’s More Than Just a Number

When the calculator tells you that you are “15 weeks and 4 days” pregnant, it means more than just a number. It tells you:

What Developmental Stage Your Baby is In: At 15 weeks, your baby might be the size of an apple and its bones are beginning to harden.
Upcoming Milestones: You can see when the next important scan (like the anatomy scan) or doctor’s visit is approaching.
Which Trimester You’re In: It helps you track your trimester, which is important for understanding your symptoms and physical changes.

Part 5: Important Considerations and Limitations

Accuracy Depends on the Due Date: The accuracy of this calculator is entirely dependent on the accuracy of the due date you enter. Always use the most recent due date given to you by your doctor.
Not a Substitute for Medical Advice: This tool is for tracking and informational purposes. It cannot replace the monitoring and check-ups performed by your doctor.
Due Dates Can Be Adjusted: Occasionally, a doctor might slightly adjust your due date based on later ultrasounds. Always use the latest date provided by your healthcare professional.

Conclusion: Stay Connected to Your Journey Every Day

Dr. Anuja Dokras’s Final Message:“A calculator that determines your gestational age from your due date is a wonderful companion for women who want to stay actively connected to every stage of their journey. It helps give you clarity, confidence, and a deeper connection to your baby’s development. Use it to track your progress and enjoy every week of your pregnancy.”

Disclaimer: This article and the calculator described within are for general informational and estimation purposes only. It should not be considered a substitute for professional medical advice. Always consult with your doctor for your pregnancy care and for accurate information.

FAQ

You only need one piece of information: your Estimated Due Date (EDD) provided by your doctor.

This calculator is specifically for women for whom an LMP-based calculation may not be accurate, such as:

Those who don’t remember their LMP.
Those with irregular periods.
Those whose due date was determined by an IVF procedure or a first-trimester ultrasound (which is the most accurate method).

Always trust the due date given by your doctor based on your first-trimester ultrasound. An ultrasound measures the actual size and development of the baby, whereas an LMP-based calculation is an estimate based on an average 28-day cycle. According to Dr. Anuja Dokras, “The first-trimester ultrasound is the ‘gold standard’ for dating a pregnancy.”

It performs a simple reverse calculation. It knows that a full-term pregnancy is 280 days (40 weeks). It determines the estimated start date of your pregnancy by counting back 280 days from your due date. Then, it counts the days from that start date to today and converts them into weeks and days.

Yes, this can occasionally happen, but it’s not common. Typically, doctors will stick with the due date determined by the first-trimester ultrasound. If any adjustments are made later, you should always use the most recent due date provided by your doctor to track your progress.

This information helps you in several ways:

Track your baby’s development: You can look up what milestones your baby is reaching in that specific week on pregnancy apps or websites.
Prepare for doctor’s appointments: You know which tests or check-ups are coming up.
Understand your symptoms: You can understand if what you are feeling is normal for that particular week.