Baby Due Date Calculator — Pregnancy Due Date Guide
The moment you find out you are pregnant, one question takes over everything else — when is my baby due? Calculate your pregnancy due date instantly using your last period, conception date, or ultrasound results. Track your pregnancy week by week with confidence.
Your due date is more than just a number on a calendar. It tells you how far along you are, which trimester you are in, how many weeks of pregnancy remain, and when to expect the most important prenatal appointments. It is the foundation of your entire pregnancy timeline.
Whether you are looking for a baby due date calculator, a pregnancy due date calculator, or a pregnancy delivery date calculator, this guide explains everything you need to know. You will learn how to calculate pregnancy due date using three different methods, understand your results, and track your pregnancy week by week.
What Is a Baby Due Date Calculator
A baby due date calculator is a free online tool that estimates the date your baby will be born based on information you provide about your pregnancy. Depending on what you know, you can use your last menstrual period, your conception date, or an ultrasound result to get your estimated due date.
The result is called an Estimated Due Date or EDD. This is not a guaranteed delivery date; it is a clinically calculated estimate that gives you and your healthcare provider a reliable reference point for planning your prenatal care.
A pregnancy calculator due date tool works the same way — some people search for it by this name, while others call it a pregnancy due date calculator, a pregnancy delivery date calculator, or simply a due date calculator. All of these terms refer to the same type of tool, and our calculator covers all of them in one place.
What a Good Pregnancy Due Date Calculator Shows You
A comprehensive pregnancy due date calculator does not just show one date. It gives you a complete picture of your pregnancy, including your estimated due date, your current pregnancy week, how many days remain until delivery, and your current trimester. This transforms a simple date tool into a full pregnancy progress tracker.
How to Calculate Pregnancy Due Date from Last Menstrual Period
The Last Menstrual Period method, commonly called the LMP method, is the most widely used way to calculate a pregnancy due date. It is the default method used by doctors, midwives, and healthcare systems worldwide.
How the LMP Method Works
The calculation is based on a straightforward formula. Your estimated due date is 280 days, or 40 weeks, from the first day of your last menstrual period.
The reason pregnancy is counted from the LMP rather than from conception is that most women know the date their last period started, but very few know the exact date of conception. Counting from the LMP gives a consistent, easy-to-use starting point that healthcare providers can rely on.
The LMP Formula
First day of last menstrual period plus 280 days equals estimated due date.
For example, if the first day of your last period was January 1, 2026, your estimated delivery date would be October 8, 2026.
When the LMP Method Is Most Accurate
The LMP method works best when your menstrual cycle is regular, typically around 28 days, and when ovulation occurs around day 14 of your cycle. If your cycles are longer, shorter, or irregular, the LMP method may give an estimate that is off by a week or more.
In those cases, using the conception date method or an ultrasound result gives a more accurate result.
How to Use the Pregnancy Delivery Date Calculator with LMP
Enter the first day of your last menstrual period into the calculator. The tool automatically adds 280 days and shows your estimated due date, your current pregnancy week, your current trimester, and the number of days remaining until your delivery date.
Conception Due Date Calculator: How to Use Conception Date
The conception due date calculator method is more precise than the LMP method for women who know when they conceived, either because they were tracking ovulation, using fertility monitoring, or had assisted conception.
How the Conception Date Method Works
Conception typically occurs about 14 days after the first day of the last menstrual period in a standard 28-day cycle. This means the conception date and the LMP date are always approximately two weeks apart.
The formula for calculating the due date from conception is different from the LMP method.
Conception date plus 266 days equals the estimated due date.
The reason this uses 266 days instead of 280 is that it counts from the actual day of fertilization, not from the LMP. Since conception is about 14 days after LMP, the two formulas produce the same result when your cycle is exactly 28 days.
Example
If your conception date was January 15, 2026, add 266 days. Your estimated due date would be October 8, 2026 — the same result as the LMP method, assuming a standard 28-day cycle.
When the Conception Due Date Calculator Is More Accurate
If you have been tracking your ovulation, using ovulation predictor kits, or know the exact date of conception through fertility treatment, the conception due date calculator gives you a more reliable estimate than relying on your LMP alone. Women with irregular cycles, longer cycles, or those who conceived through assisted reproduction.
How to Use the Calculator with Conception Date
Enter your conception date into the pregnancy due date calculator. The tool adds 266 days and displays your estimated due date, current pregnancy week, trimester, and remaining days until delivery.
How to Calculate Pregnancy Due Date from Ultrasound
The ultrasound method is considered the most accurate way to estimate a due date — especially when it is performed in the first trimester. It is particularly useful for women who are unsure of their LMP or who have irregular cycles.
How the Ultrasound Method Works
During an ultrasound examination, the healthcare provider measures the size of the embryo or fetus. In the first trimester, this is typically done using the crown-rump length — a measurement from the top of the head to the bottom of the baby. This measurement is compared to established growth charts to determine the gestational age in weeks and days.
Once the gestational age is confirmed by the ultrasound, the due date is calculated by counting forward to 40 weeks from the clinical start date.
Why First Trimester Ultrasound Is Most Accurate
First-trimester ultrasounds, typically performed between 6 and 13 weeks, are the most reliable for dating because early fetal growth is very consistent across all pregnancies. All babies at 8 weeks are approximately the same size regardless of genetics or other factors, which makes the measurement highly accurate for age estimation.
Later ultrasounds become less accurate for dating because babies grow at different rates as pregnancy progresses; some are naturally larger, some smaller, and the measurement is no longer a reliable indicator of gestational age.
How to Use the Baby Due Date Calculator with Ultrasound
Enter the date of your ultrasound scan and the gestational age shown on your ultrasound report, for example, 8 weeks and 3 days. The pregnancy calculator due date tool uses this information to work back to the clinical start date and then forward to your estimated due date, current pregnancy week, trimester, and remaining days until delivery.
Pregnancy Week Calculator by Due Date
Once your baby due date calculator gives you a result, you can also use it as a pregnancy week calculator by due date, meaning you can work backwards from the due date to find out exactly which week of pregnancy you are currently in and how many weeks remain.
Here is what each piece of information means for your pregnancy.
Estimated Due Date
Your estimated due date is the date your baby is most likely to be born, calculated as 40 weeks from the start of your last menstrual period or adjusted based on conception date or ultrasound results. Only about 4 to 5 percent of babies are born on their exact estimated due date. Most babies arrive within one to two weeks before or after this date, which is completely normal. Think of your due date as the center of a window, not a fixed deadline.
Current Pregnancy Week
Your current pregnancy week tells you exactly how far along you are at this moment. Pregnancy weeks are counted from the first day of your last menstrual period, which means you are technically considered pregnant before conception even occurs. This clinical standard is used by all healthcare providers worldwide and ensures consistent communication between patients and doctors.
Using the pregnancy week calculator by due date feature, you can also work in reverse. If you already know your due date, the tool automatically calculates your current week and trimester.
Current Trimester
Pregnancy is divided into three trimesters, each covering a different stage of your baby’s development and your body’s changes.
The first trimester runs from week 1 to the end of week 12. This is when major organ development occurs. Most women experience symptoms like nausea, fatigue, and breast tenderness during this stage.
The second trimester runs from week 13 to the end of week 26. This is often called the comfortable trimester, where nausea typically eases, energy returns, and you begin to show. Your baby grows rapidly and becomes more active.
The third trimester runs from week 27 to week 40 and beyond. Your baby continues to grow and prepare for birth. You may experience back pain, frequent urination, and difficulty sleeping as your delivery date approaches.
Remaining Days Until Delivery
The remaining days count gives you a real-time countdown to your estimated delivery date. This number decreases every day and helps you track your pregnancy progress in a concrete, tangible way, especially useful for planning maternity leave, hospital tours, and birth preparation classes.
How Accurate Is a Pregnancy Due Date Calculator
A pregnancy delivery date calculator gives you a highly reliable estimate, but it is important to understand what factors affect its accuracy.
Factors That Affect Accuracy
Cycle length is the most significant variable for the LMP method. The standard formula assumes a 28-day cycle with ovulation on day 14. Women with longer or shorter cycles may get a result that is off by several days.
Irregular periods are another factor. If your menstrual cycle varies significantly from month to month, the LMP method may not give you an accurate starting point. In this case, using a conception due date calculator gives better results.
Ultrasound timing makes a big difference. A first-trimester ultrasound is significantly more accurate than a second or third-trimester scan for estimating gestational age. If your first ultrasound was done after 14 weeks, the result may differ from the LMP-based estimate.
Individual pregnancy variation also plays a role. Every pregnancy is different, and the actual length can naturally range from 37 to 42 weeks, all of which are considered normal.
What the Research Says
According to the American College of Obstetricians and Gynecologists, a first-trimester ultrasound is the most accurate method for confirming gestational age. If the ultrasound result differs from the LMP-based estimate by more than 7 days, most providers will adjust the due date to match the ultrasound finding.
Your healthcare provider may update your estimated due date after your first prenatal ultrasound, which typically happens between 8 and 12 weeks. This is completely normal; it simply means the estimate is being refined with better data.
Can Your Due Date Change After an Ultrasound
Yes, your due date can be updated, and this is a routine part of prenatal care.
The most common reason for a due date change is when the first trimester ultrasound shows a gestational age that differs significantly from the LMP-based estimate. If this difference is more than 7 days, your healthcare provider will typically adjust the due date to align with the ultrasound measurement.
A due date change does not mean anything is wrong with your pregnancy. It simply means the pregnancy calculator due date estimate was slightly off, and the ultrasound has given a more precise result.
Once a due date is established from a first-trimester ultrasound, it is generally not changed again based on later scans. Later ultrasounds are less reliable for dating because babies grow at different individual rates in the second and third trimesters.
Pregnancy Week by Week — Key Milestones
Here is a brief overview of important milestones to look forward to during your pregnancy.
Weeks 6 to 8 — First Heartbeat
A heartbeat can typically be detected on ultrasound for the first time, the most emotional moment of early pregnancy for many parents.
Weeks 10 to 13 — First Trimester Screening
The first trimester screening takes place, including a nuchal translucency ultrasound that checks for chromosomal conditions.
Weeks 18 to 20 — Anatomy Scan
The anatomy scan provides a detailed look at your baby’s development and is when many parents find out the baby’s sex.
Week 24 — Viability Milestone
Your baby is considered viable, meaning survival outside the womb becomes possible with medical support.
Week 28 — Third Trimester Begins
Your baby’s brain is developing rapidly, and they can hear sounds from outside the womb. You enter the final stretch of pregnancy.
Weeks 36 to 37 — Early Term
Your baby is considered early term. Most providers will schedule a Group B Strep test around this time.
Weeks 39 to 40 — Full Term & Delivery
Your baby is full term, and your delivery date arrives. If labor has not started by 41 or 42 weeks, your healthcare provider will discuss induction options.
Pregnancy Due Date Calculator FAQ
Calculate Your Due Date Today
Your due date is more than just a number on a calendar. It tells you how far along you are, which trimester you are in, how many weeks of pregnancy remain, and when to expect the most important prenatal appointments. It is the foundation of your entire pregnancy timeline.