Due Date Calculator
Use our free Due Date Calculator to estimate your baby’s expected due date based on the first day of your last menstrual period (LMP) and your average menstrual cycle length.
Enter the first day of your last period, adjust the cycle length if your cycle is different from the typical 28 days, and select Calculate Due Date to get your estimated due date.
Your estimated due date can help you understand how far along your pregnancy may be and when your baby is expected to arrive. However, a due date is an estimate, not a guaranteed delivery date. Only a small percentage of babies are born exactly on their estimated due date.
Important: This calculator provides an estimate for informational purposes. Your healthcare provider may adjust your estimated due date after reviewing your medical history and performing an ultrasound examination.
Due Date Calculator
PregnancyHow Does the Due Date Calculator Work?
Our calculator uses the first day of your last menstrual period (LMP) as the starting point and applies Naegele’s Rule, adjusted for your menstrual cycle length.
A typical pregnancy lasts about 40 weeks, or 280 days, from the first day of the last menstrual period.
The calculator starts with your LMP and estimates when 40 weeks of pregnancy will be completed. If your average menstrual cycle is longer or shorter than 28 days, the calculator adjusts the estimate accordingly.
Basic Calculation
Estimated due date = First day of LMP + 280 days
For a standard 28-day cycle, this provides the traditional estimated due date.
If your cycle differs from 28 days, the calculation can be adjusted to account for the difference.
For example, if your cycle is longer than 28 days, ovulation may occur later than the typical day 14. The estimated due date may therefore move later. A shorter cycle may shift the estimate earlier.
This calculation works best when you know the first day of your last period and your cycles are reasonably regular.
How to Use Our Due Date Calculator
Calculating your estimated due date takes only a few steps.
Step 1: Enter the First Day of Your Last Period
Select the date when your last menstrual period began.
Use the first day of actual menstrual bleeding rather than the day your period ended.
Step 2: Enter Your Cycle Length
The calculator uses 28 days as the default cycle length.
If your menstrual cycle normally lasts longer or shorter than 28 days, enter your average cycle length for a more personalized estimate.
If you are unsure about your average cycle length, you can use 28 days as a starting point, but remember that your actual ovulation date may have been different.
Step 3: Calculate Your Due Date
Click Calculate Due Date to receive your estimated due date.
The result gives you a useful starting point for tracking your pregnancy timeline.
What Is a Due Date?
Your estimated due date (EDD) is the date on which your pregnancy is expected to reach approximately 40 weeks.
It is important to understand that the due date does not predict the exact day your baby will be born.
Pregnancy length varies between individuals, and labor can begin before or after the estimated due date. Your healthcare provider will monitor your pregnancy and help determine whether your estimated due date remains appropriate.
Think of your due date as a planning milestone, not a deadline.
How Accurate Is a Due Date Calculator?
A due date calculator can provide a useful estimate, but it cannot predict your baby’s exact birth date.
The accuracy of an LMP-based calculation depends on several factors, including:
- How accurately you remember the first day of your last period
- Whether your menstrual cycles are regular
- Whether your cycle length differs from the typical 28 days
- When you actually ovulated
- Whether you experienced bleeding that was mistaken for a period
- When conception occurred
Ovulation does not always happen on the same day for every person or in every cycle. This can make an LMP-based due date less precise, particularly for people with irregular cycles.
For this reason, your healthcare provider may use an early pregnancy ultrasound to help establish or confirm the pregnancy dating.
Why Does Cycle Length Matter?
The standard due date calculation assumes a 28-day menstrual cycle, with ovulation occurring around the middle of the cycle.
In reality, cycle lengths vary.
If your average cycle is longer than 28 days, you may ovulate later than someone with a 28-day cycle. If your cycle is shorter, you may ovulate earlier.
This is why our calculator allows you to enter your cycle length rather than relying only on a fixed 28-day assumption.
However, cycle length alone cannot determine the exact day you ovulated. If your cycles are irregular, the LMP method may be less reliable.
What If I Don't Remember My Last Period?
If you cannot remember the first day of your last menstrual period, do not guess if you can avoid it.
Your healthcare provider may use other information to estimate your pregnancy dates, including:
- Early ultrasound measurements
- Your menstrual history
- The timing of possible conception
- Previous pregnancy information
An early ultrasound can be particularly helpful when your LMP is uncertain or your menstrual cycles are irregular.
If you do not know your LMP, contact your healthcare provider rather than relying on an inaccurate date entered into a calculator.
How Many Weeks Pregnant Am I?
Pregnancy is usually measured from the first day of your last menstrual period, not from the day of conception.
This means pregnancy dating traditionally begins about two weeks before ovulation and conception occur in a typical cycle.
For example, when you are described as being 8 weeks pregnant, the pregnancy is generally dated as eight weeks from the first day of your last menstrual period.
This system may seem confusing because conception usually occurs later, but healthcare professionals use it as a standardized way to date pregnancy.
Your healthcare provider may revise your pregnancy dates if an ultrasound provides a more appropriate estimate.
Understanding the Three Trimesters
Pregnancy is commonly divided into three trimesters.
First Trimester
The first trimester covers the early stage of pregnancy, when major developmental changes begin.
Many people experience symptoms such as nausea, tiredness, breast tenderness, and increased urination during this stage, although every pregnancy is different.
Second Trimester
The second trimester is often associated with noticeable changes in the body and continued fetal growth.
Some pregnancy symptoms may improve during this period, although experiences vary from person to person.
Third Trimester
The third trimester is the final stage of pregnancy leading toward birth.
During this time, your healthcare provider will continue monitoring your health and your baby’s development and prepare you for labor and delivery.
Your healthcare provider can give you the most accurate information about your current pregnancy week and trimester based on your confirmed pregnancy dates.
Due Date vs. Conception Date
Your estimated due date and conception date are not the same.
The due date is typically calculated from the first day of your last menstrual period. Conception usually occurs later, around the time of ovulation.
Because sperm can survive for several days in the reproductive tract and ovulation can vary between cycles, it is often difficult to identify the exact day of conception without specific fertility tracking information.
This is why healthcare providers generally use pregnancy dating methods rather than trying to determine an exact conception date.
Why Can an Ultrasound Change My Due Date?
An ultrasound may result in a different estimated due date than the date calculated from your LMP.
- This can happen because:
- You ovulated earlier or later than expected.
- Your menstrual cycle was not 28 days.
- Your cycle was irregular.
- You remembered your LMP incorrectly.
- The bleeding you recorded was not a typical menstrual period.
- An early ultrasound can help estimate pregnancy age by measuring the developing embryo or fetus.
Your healthcare provider will decide whether your original LMP-based date or an ultrasound-based date provides the most appropriate estimate for your pregnancy.
Do not change your medical care or pregnancy schedule based solely on an online calculator.
Can My Baby Arrive Before or After the Due Date?
Yes. The estimated due date represents a target date, not an exact prediction.
Many healthy babies arrive before or after their estimated due date. Your healthcare provider will monitor your pregnancy as you approach the end of your estimated pregnancy period and advise you about the appropriate next steps.
If you experience signs of labor or have concerns about your pregnancy, contact your healthcare provider or maternity unit for guidance.
What Should I Do After Calculating My Due Date?
Once you have your estimated due date, use it as a reference point for planning your prenatal care.
You can:
- Schedule or confirm your prenatal appointments.
- Keep track of your pregnancy week.
- Discuss recommended prenatal tests with your healthcare provider.
- Learn about pregnancy nutrition and healthy habits.
- Prepare questions for your next prenatal visit.
- Plan ahead for your delivery and newborn care.
Your healthcare provider should remain your primary source for personalized pregnancy advice and medical decisions.
Due Date Calculator FAQs
The calculator uses the first day of your last menstrual period and estimates a pregnancy length of approximately 40 weeks. It adjusts the estimate when you enter a menstrual cycle length that differs from the standard 28-day cycle.
Naegele’s Rule is a traditional method for estimating a due date from the first day of the last menstrual period. It generally adds 280 days, or 40 weeks, to the LMP date and can be adjusted for cycle length.
A longer cycle may mean that you ovulate later than the typical day 14. Our calculator allows you to enter your average cycle length to adjust the estimated due date. However, this remains an estimate because cycle length does not tell us the exact day ovulation occurred.
The LMP method may be less accurate when your menstrual cycles are irregular. An early ultrasound may provide a more reliable estimate of pregnancy dating. Speak with your healthcare provider if you are unsure about your pregnancy dates.
No. A due date calculator estimates when your pregnancy may reach approximately 40 weeks. It cannot predict the exact day your baby will be born.
Yes. Your healthcare provider may adjust your estimated due date if an ultrasound provides a different and more reliable estimate of pregnancy age.
Pregnancy is generally dated from the first day of your last menstrual period. Enter your LMP into the calculator to estimate your due date and use that date to track your pregnancy timeline.
If you cannot remember your LMP, avoid entering an inaccurate date. Your healthcare provider can help estimate your pregnancy dates using your medical history and, when appropriate, ultrasound measurements.
Pregnancy dating after IVF or other assisted reproductive treatments may use the embryo transfer date and the age of the embryo rather than relying only on the LMP. If you conceived through IVF, follow the pregnancy dating provided by your fertility specialist or healthcare provider.
