What is the best way to calculate my due date?

The most accurate way to calculate your due date is through a first-trimester ultrasound (before 14 weeks). If you know your last menstrual period (LMP) date and have regular cycles, the LMP method is also reliable. For irregular cycles, IVF pregnancies, or uncertain dates, ultrasound dating is essential for accuracy.

How many weeks pregnant am I based on my last period?

To calculate how many weeks pregnant you are, count from the first day of your last menstrual period (LMP). Pregnancy is typically 40 weeks (280 days) from your LMP. Our pregnancy week calculator helps you determine your exact week and day of pregnancy instantly.

When will I feel my baby move (quickening)?

First-time mothers typically feel baby's first movements (quickening) between 18-22 weeks of pregnancy. Mothers who have been pregnant before may feel movements earlier, around 16 weeks. Early movements feel like flutters, bubbles, or gentle rolling sensations.

What is considered full term pregnancy?

According to medical definitions: Early term is 37-38 weeks, full term is 39-40 weeks, late term is 41 weeks, and post-term is 42 weeks or beyond. The optimal time for delivery is 39-40 weeks when the baby has fully matured and risks are lowest.

How is the due date calculated for IVF pregnancy?

For IVF pregnancies, the due date calculation is more precise. We subtract the embryo age at transfer plus 14 days from 280 days. For example, a day 5 embryo transfer means we add 266 days minus 5 days to your transfer date. IVF due dates are typically very accurate.

Pregnancy Due Date Calculator – FREE & Accurate EDD

Pregnancy Due Date Calculator: Estimate Your Baby’s Arrival

Finding out you’re pregnant is one of life’s most exciting moments—and one of the first questions on every expectant parent’s mind is, “When will my baby arrive?” A pregnancy due date calculator helps you estimate your baby’s arrival by using key information like your last menstrual period, conception date, or ultrasound results.

Understanding your due date isn’t just about marking a calendar. It helps you and your healthcare provider track your baby’s development, schedule important prenatal appointments, and prepare emotionally and practically for your little one’s arrival. Whether you’re in the very early stages of pregnancy or already planning your nursery, knowing how your due date is determined empowers you to make informed decisions throughout your journey.

This guide will walk you through everything you need to know about calculating your pregnancy due date, understanding gestational age, and navigating the week-by-week progression of pregnancy.

What Is a Pregnancy Due Date Calculator?

A pregnancy due date calculator is a tool that estimates the day your baby is most likely to be born. It’s based on well-established medical formulas that calculate gestational age—the time measured from the first day of your last menstrual period to the current date.

Your estimated due date (EDD) represents the completion of approximately 40 weeks of pregnancy. While most babies aren’t born exactly on their due date, this estimate creates a framework for monitoring your baby’s growth and development throughout pregnancy. Healthcare providers use this date to schedule ultrasounds, blood tests, and other screenings at the appropriate times.

Understanding your due date also helps you prepare practically—planning maternity leave, arranging childcare for other children, and getting your home ready for a newborn all benefit from having a target timeline.

How Is Pregnancy Due Date Calculated? The Medical Method

The standard medical approach to calculating pregnancy uses Naegele’s Rule, developed in the 1800s and still widely used today. This rule assumes a typical menstrual cycle of 28 days with ovulation occurring on day 14.

Here’s how it works:

Naegele’s Rule Formula:

Take the first day of your last menstrual period (LMP)
Add 7 days
Subtract 3 months
Add 1 year (if necessary)

For example, if your last period started on January 10, you would add 7 days (January 17), subtract 3 months (October 17), and your estimated due date would be October 17 of the same year.

This calculation gives you a full-term pregnancy of approximately 40 weeks or 280 days from your LMP. The American College of Obstetricians and Gynecologists (ACOG) recognizes this as the standard method when an accurate LMP date is known.

It’s important to understand that pregnancy isn’t actually 9 months—it’s closer to 10 months when counted in calendar months. This is because pregnancy is measured in weeks (40 weeks), and months vary in length.

5 Methods for Calculating Your Pregnancy Due Date

Different situations call for different calculation methods. Here are the five main approaches healthcare providers use:

1. Last Menstrual Period (LMP) Method

This is the most common starting point for dating a pregnancy. If you have regular menstrual cycles and remember the first day of your last period, this method provides a reliable baseline estimate.

Best for: Women with regular 28-day cycles who track their periods

Accuracy: Good initial estimate, often confirmed or adjusted by ultrasound

2. Conception Date Method

If you know exactly when conception occurred—perhaps you were tracking ovulation or only had intercourse on specific dates—you can calculate your due date from that point. A conception date calculator adds 266 days (38 weeks) from the conception date, since conception typically occurs about 2 weeks after your LMP.

Best for: Women who tracked ovulation or had limited opportunities for conception

Accuracy: Very accurate if conception date is certain

3. Reverse Due Date Calculation

Sometimes you already know your due date from a healthcare provider but want to calculate backward to determine your pregnancy start date or conception window. A reverse due date calculator works backward from your EDD to estimate when conception likely occurred.

Best for: Planning purposes or understanding your conception timeframe

Accuracy: As accurate as the due date it’s based on

4. Ultrasound Dating

Early pregnancy ultrasounds (performed between 8-13 weeks) are the most accurate way to date a pregnancy. Measurements of the embryo or fetus at this stage are remarkably consistent across all pregnancies, making them more reliable than LMP dating, especially if you have irregular cycles or can’t remember your last period.

Your healthcare provider measures specific parameters like crown-rump length to determine gestational age with precision. If the ultrasound date differs significantly from your LMP calculation, your provider will typically use the ultrasound date.

Best for: Everyone, especially those with irregular cycles or uncertain LMP

Accuracy: Most accurate method, especially in the first trimester

5. IVF and IUI Pregnancies

Assisted reproduction pregnancies have the most precise dating because the conception date is exactly known. An IVF due date calculator accounts for the specific embryo transfer date and embryo age (3-day or 5-day embryo).

Similarly, an IUI due date calculator uses the insemination date to calculate your due date with exceptional accuracy since the fertilization window is very specific.

Best for: Anyone who conceived through fertility treatments

Accuracy: Extremely accurate due to known fertilization timing

Understanding Pregnancy Week-by-Week

One of the most confusing aspects of pregnancy is understanding how weeks are counted. You’re actually “pregnant” for about 38 weeks from conception, but pregnancy is measured as 40 weeks from your LMP—meaning you’re counting two weeks before conception even happened!

Here’s why: Since most women don’t know their exact conception date, and the LMP is easy to identify, the medical community standardized on LMP dating. Your pregnancy officially “starts” on the first day of your last period, even though conception doesn’t occur until about two weeks later.

How to Calculate Your Current Pregnancy Week

To know where you are week-by-week:

Count the number of days from the first day of your LMP to today
Divide by 7 to get weeks
The remainder represents additional days

For example, if 156 days have passed since your LMP, you’re 22 weeks and 2 days pregnant (156 ÷ 7 = 22 weeks with 2 days remaining).

Your pregnancy is divided into specific milestones:

Weeks 1-13: First trimester
Weeks 14-27: Second trimester
Weeks 28-40+: Third trimester

Each week brings new developments, which is why tracking pregnancy week-by-week helps you understand your baby’s growth and what symptoms you might experience.

Converting Pregnancy Weeks to Months

Many people want to know their pregnancy in terms of months rather than weeks. The conversion isn’t perfectly neat because pregnancy months don’t align perfectly with calendar months.

Here’s a general guide for converting weeks to months:

First Trimester:

Weeks 1-4: Month 1
Weeks 5-8: Month 2
Weeks 9-13: Month 3

Second Trimester:

Weeks 14-17: Month 4
Weeks 18-22: Month 5
Weeks 23-27: Month 6

Third Trimester:

Weeks 28-31: Month 7
Weeks 32-35: Month 8
Weeks 36-40: Month 9
Week 40+: Month 10

Yes, pregnancy is actually 10 months when you count it this way! A pregnancy month calculator can help you translate between weeks and months, though most healthcare providers use weeks for precision.

How Trimesters Are Calculated in Pregnancy

Pregnancy is divided into three trimesters, each approximately 13-14 weeks long. These divisions represent distinct phases of fetal development and maternal experience:

First Trimester (Weeks 1-13):

This period covers early development when all major organs form. Many women experience morning sickness, fatigue, and emotional changes. First trimester ultrasounds establish accurate dating and confirm viability.

Second Trimester (Weeks 14-27):

Often called the “honeymoon phase” of pregnancy, this trimester brings increased energy and the exciting milestone of feeling your baby move. Anatomy scans occur around week 20.

Third Trimester (Weeks 28-40+):

The final stretch focuses on your baby’s growth and lung maturity. You’ll have more frequent prenatal visits as your due date approaches. Full term begins at 37 weeks, though 40 weeks remains the target for optimal outcomes.

Understanding which trimester you’re in helps you anticipate changes and prepare for upcoming milestones.

When Can I Take a Pregnancy Test?

Knowing when to take a pregnancy test is crucial for getting accurate results. The timing depends on your body’s production of hCG (human chorionic gonadotropin), the pregnancy hormone that tests detect.

Best Timing:

Earliest: 10-12 days after conception (before your missed period)
Most accurate: First day of your missed period or later
After IVF/IUI: Follow your clinic’s specific instructions, typically 9-14 days after transfer or insemination

An implantation calculator can help you understand when implantation likely occurred, since hCG production begins after the embryo implants in your uterus.

Testing too early increases the risk of a false negative—you might be pregnant, but hCG levels aren’t high enough for detection yet. Learn more about timing and accuracy through resources on pregnancy test accuracy.

If you test negative but still suspect pregnancy (late period, pregnancy symptoms), wait a few days and test again. HCG doubles approximately every 48-72 hours in early pregnancy.

Who Should Use a Pregnancy Due Date Calculator?

A pregnancy due date calculator is helpful for:

Women who just received a positive pregnancy test and want to understand their timeline before their first prenatal appointment
Those tracking fertility who know their ovulation or conception date and want to calculate their due date independently
Parents planning ahead for work schedules, childcare, or other children’s needs
Anyone with irregular cycles who needs a starting point before ultrasound dating
IVF or IUI patients who want to calculate their specific due date based on transfer or insemination dates
Women curious about their conception date based on a known due date

Even if you use a calculator, remember that your healthcare provider will establish your official due date, typically confirmed by first trimester ultrasound.

Accuracy and Limitations of Due Date Calculators

While pregnancy due date calculators are valuable tools, it’s important to understand their limitations:

Accuracy Factors:

LMP-based calculations assume a 28-day cycle with day 14 ovulation, which doesn’t apply to everyone
Irregular cycles, recent birth control use, or breastfeeding can affect accuracy
Only about 5% of babies arrive on their exact due date
Most babies are born between 37-42 weeks (full term range)

Most Accurate Method:

First trimester ultrasound (8-13 weeks) provides the most accurate dating, with precision within 3-5 days. If you have irregular cycles or uncertain dates, ultrasound dating should be considered the gold standard.

Your Due Date May Change:

It’s not uncommon for your due date to be adjusted after an early ultrasound, especially if it differs from your LMP calculation by more than 5-7 days. This doesn’t mean something is wrong—it simply means the ultrasound measurement provides more accurate dating.

Remember that your due date is an estimate, not a deadline. A full-term pregnancy ranges from 37 to 42 weeks, and your baby will arrive when ready. Use your due date as a guide for preparation rather than an exact prediction.

Medical Disclaimer

This pregnancy due date calculator and the information provided on this website are for educational and informational purposes only. They are not intended to replace professional medical advice, diagnosis, or treatment.

Always consult your qualified healthcare provider with any questions about your pregnancy, prenatal care, or due date. Every pregnancy is unique, and only your doctor or midwife can provide personalized medical guidance based on your individual health history and circumstances.

If you experience any concerning symptoms during pregnancy—such as bleeding, severe pain, decreased fetal movement, or other urgent issues—contact your healthcare provider immediately or seek emergency medical attention.

Frequently Asked Questions About Pregnancy Due Date Calculators

How do I calculate my pregnancy week?

To calculate your current pregnancy week, count the number of days from the first day of your last menstrual period to today, then divide by seven. For example, 70 days from your LMP means you’re 10 weeks pregnant. Most calculators do this math automatically, but understanding the method helps you track your progress independently.

How accurate is a pregnancy due date calculator?

LMP-based calculators are reasonably accurate for women with regular 28-day cycles, but only about 5% of babies arrive on their exact due date. First trimester ultrasound is the most accurate method, typically precise within 3-5 days. Due date calculators provide an estimate rather than an exact prediction, helping you and your healthcare provider monitor your baby’s development.

How is pregnancy month calculated from weeks?

Converting weeks to months isn’t exact because pregnancy “months” are about 4-4.5 weeks rather than calendar months. Generally, weeks 1-13 are months 1-3 (first trimester), weeks 14-27 are months 4-6 (second trimester), and weeks 28-40 are months 7-10 (third trimester). Yes, pregnancy is actually 10 months, not 9, when calculated this way!

How many weeks are in a full pregnancy?

A full-term pregnancy is 40 weeks from the first day of your last menstrual period, which equals 280 days or approximately 10 months. However, “full term” actually ranges from 37 weeks to 42 weeks. Babies born between 37-39 weeks are considered early term, 39-40 weeks is full term, and 40-42 weeks is late term.

When can I take a pregnancy test after conception?

You can take a sensitive early detection pregnancy test about 10-12 days after conception, though waiting until the first day of your missed period (approximately 14 days post-conception) provides the most accurate results. Testing too early increases the risk of false negatives because hCG levels may not be high enough to detect yet.

How is IVF pregnancy due date calculated?

IVF pregnancies have the most precise dating because the embryo transfer date is known exactly. For a 5-day embryo (blastocyst), you subtract 19 days from the transfer date to find your “LMP” equivalent, then add 280 days. For a 3-day embryo, subtract 17 days from transfer. This accounts for the exact age of the embryo at transfer.

What is the difference between gestational age and fetal age?

Gestational age is measured from the first day of your last menstrual period and is what healthcare providers use for dating (typically 40 weeks). Fetal age (or conceptional age) is measured from actual conception, typically two weeks after your LMP, making it about 38 weeks for a full-term pregnancy. Medical professionals use gestational age as the standard.

Why do doctors use last menstrual period for dating?

Doctors use LMP dating because it’s a reliable reference point that most women can identify. Since the exact conception date is usually unknown (sperm can survive 3-5 days, and ovulation timing varies), LMP provides a consistent starting point. This standardized approach has been used successfully for decades, though it’s often confirmed or adjusted with ultrasound.

Can my due date change during pregnancy?

Yes, your due date may be adjusted after an early ultrasound if the measurement differs significantly (usually more than 5-7 days) from your LMP-based calculation. First trimester ultrasounds are very accurate, so if there’s a discrepancy, your provider will typically update your due date based on the ultrasound. After 20 weeks, due dates are rarely changed.

How does ultrasound determine pregnancy due date?

Early ultrasounds (8-13 weeks) measure the crown-rump length (CRL)—the length from the top of the embryo’s head to its bottom. This measurement is remarkably consistent across all pregnancies at this stage, making it the most accurate dating method. The measurement is compared to standardized growth charts to determine gestational age within 3-5 days.

Is pregnancy really 9 months?

Not exactly. Pregnancy is 40 weeks from your LMP, which equals 280 days or about 10 months when counted as pregnancy months (4-week periods). The “9 months” figure comes from calendar months, but since pregnancy is measured more precisely in weeks, you’ll often hear healthcare providers refer to it as 40 weeks or 10 lunar months.

What if I have irregular periods—how do I calculate my due date?

If you have irregular cycles, LMP-based calculation may be inaccurate. In this case, an early ultrasound (before 13 weeks) is the best way to date your pregnancy accurately. If you were tracking ovulation, you can use your known conception date for calculation. Your healthcare provider will determine the most appropriate dating method based on your situation.

How do I calculate my due date if I don’t know my LMP?

If you don’t remember your last period, your healthcare provider will rely on an early ultrasound for dating. If you know approximately when you conceived, you can add 266 days (38 weeks) to that date for an estimate. Some women can also estimate based on when their pregnancy test turned positive, though this is less precise.

Does the due date calculator work for twins?

Standard due date calculators work for twin pregnancies, giving you the 40-week mark from your LMP or conception date. However, twins are often born earlier—the average twin pregnancy lasts about 35-37 weeks. Your healthcare provider will monitor your pregnancy closely and may adjust expectations based on your specific situation and whether you have identical or fraternal twins.

How is IUI due date different from natural conception?

IUI due date calculation is more precise than natural conception dating because you know exactly when insemination occurred. Your due date is calculated by adding 266 days (38 weeks) to your IUI date, since insemination happens during your fertile window when conception would occur. This is typically more accurate than LMP-based dating.

What happens if I go past my due date?

Going past your due date is common—most providers allow pregnancy to continue until 41-42 weeks before discussing induction, as long as both mother and baby are healthy. Your provider will monitor you more frequently with ultrasounds and non-stress tests. Post-term pregnancy (beyond 42 weeks) carries increased risks, so induction is typically recommended before reaching that point.

How early can pregnancy be detected by ultrasound?

A transvaginal ultrasound can detect a gestational sac as early as 4.5-5 weeks from your LMP (about 2.5-3 weeks after conception). A fetal heartbeat can usually be seen by 6-7 weeks. However, dating ultrasounds are most accurate between 8-13 weeks when measurements are more precise and consistent.

Should I use LMP or conception date for calculating due date?

If you have regular cycles and know your LMP, start with that—it’s the medical standard. However, if you tracked ovulation and know your conception date precisely, that can be equally or more accurate. First trimester ultrasound remains the gold standard and will confirm or adjust either calculation. Discuss with your provider which method makes sense for your situation.

How do I calculate how far along I am?

Calculate days from the first day of your last period to today, then divide by seven. The quotient is your week number, and the remainder is extra days. For example, 100 days since your LMP equals 14 weeks and 2 days pregnant. Online calculators automate this math and can also show your progress as months or trimester stage.

What’s the difference between due date and estimated delivery date?

These terms are used interchangeably. EDD (estimated date of delivery) and due date both refer to the projected completion of 40 weeks of pregnancy. Some providers use EDD in medical records, while “due date” is more commonly used in casual conversation. Both represent the same target date for your baby’s arrival.

Ready to calculate your pregnancy due date?

Use our calculator above to get your personalized estimate and begin tracking your pregnancy journey week by week. Remember to confirm your due date with your healthcare provider at your first prenatal appointment for the most accurate timeline and comprehensive prenatal care.

Pregnancy Due Date Calculator – All In One Calculator

Select Your Pregnancy Due Date Calculation Method

How to Calculate Your Baby's Due Date - Step by Step

Your Personalized Pregnancy Timeline & Due Date

Your Pregnancy Progress Tracker

Complete Prenatal Appointment Schedule & Pregnancy Milestones

Pregnancy Trimester Milestones & Development Stages

Complete Week-by-Week Pregnancy Development Guide (Week 4-40)

Important Pregnancy Tips & Medical Guidance

Medical Disclaimer & Accuracy Information