Pregnancy Calculator

What This Calculator Does

This pregnancy due date calculator uses a simple but proven method called Naegele's rule to estimate when your baby will arrive. It's based on your Last Menstrual Period, commonly called your LMP.

Here's the math: a healthy pregnancy lasts about 280 days, or 40 weeks, from the first day of your last menstrual period. That's why doctors use LMP as the starting point, not the day you actually got pregnant (which can be hard to pinpoint). When you enter your LMP date, the calculator adds 280 days to give you your Estimated Due Date (EDD).

How Naegele's Rule Works:

1. Take your LMP date
2. Add 7 days
3. Subtract 3 months
4. Add 1 year
5. That's your due date!

The Estimated Due Date (EDD) is your expected birth date. But here's the truth: only about 5% of babies arrive exactly on their due date. Most babies come within 2 weeks before or after. Your doctor may refine this estimate with an ultrasound, which is even more accurate than calendar calculations.

Your Pregnancy Week by Week

Your 40-week pregnancy is divided into three trimesters. Each one brings different changes and milestones as your baby develops:

First Trimester (Weeks 1 to 13)

These early weeks are when the magic begins. Your baby develops from a single cell to a tiny human with a heartbeat. Weeks 1 and 2 are counted from your LMP even though you're not technically pregnant yet. By week 5, your baby's heart is beating. Week 8 is when most women take a pregnancy test and get that positive result. By week 13, your baby is about the size of a peach and has all major organs.

What you might feel: Nausea, fatigue, breast tenderness, mood swings. Many women feel exhausted and need more rest than usual.

Second Trimester (Weeks 14 to 26)

This is often called the "honeymoon trimester." Many women feel better now. Your baby starts looking recognizably human. By week 16, your doctor can usually tell the baby's sex on ultrasound. By week 20, you'll have your detailed anatomy scan where doctors check every part of your baby. Your belly grows noticeably. By week 26, your baby can hear sounds and respond to them.

What you might feel: Energy returning, showing, feeling your baby move for the first time, and a healthy appetite. This is usually the most comfortable trimester.

Third Trimester (Weeks 27 to 40)

Your baby gets bigger and heavier. By week 34, your baby weighs about 2 kg. By week 37, your baby is considered full-term (meaning they can be born safely anytime). Your baby positions themselves head-down for birth in the weeks before delivery. You'll have regular check-ups to monitor your baby's position and your health.

What you might feel: Heaviness, back pain, trouble sleeping, frequent bathroom trips, and Braxton-Hicks contractions (practice contractions). You're ready to meet your baby.

Trimester Guide at a Glance

Here's a quick reference for what happens in each trimester:

First Trimester

Weeks 1-13

Week 1-2: Counted from LMP
Week 5: Heartbeat detectable
Week 8: Positive pregnancy test
Week 12: First ultrasound screening
Week 13: Size of peach

Second Trimester

Weeks 14-26

Week 16: Gender revealed on scan
Week 18: Detailed anatomy scan
Week 16-20: First fetal movements
Week 24: Viability milestone
Week 26: Baby hears voices

Third Trimester

Weeks 27-40

Week 28: Glucose screening
Week 34: Baby weighs 2 kg
Week 36: Head-down position
Week 37: Full-term reached
Week 40: Due date

How to Use This Calculator

Using this calculator is incredibly simple. It takes less than 30 seconds:

1
Identify Your LMP Date
Think back to the first day of your last menstrual period. That's day 1 of your pregnancy counting. If you're not sure, check your calendar or ask your doctor. Your LMP is the most important number.
2
Enter the Date
Click on the date field and enter your LMP date. You can use the date picker (calendar) or type it directly. The format is easy and the field guides you.
3
Click Calculate
Hit the "Calculate Due Date" button. The calculator instantly processes your information and gives you results.
4
View Your Results
You'll see your current pregnancy week, current number of days, and your estimated due date. Bookmark this page or screenshot it for your records.

Pro tip: Run this calculator regularly as your pregnancy progresses. Each time you use it, it'll show you how many weeks you've progressed. You can watch your pregnancy move forward week by week.

Important Things to Know About Due Dates

Here's what everyone should understand about due dates:

•
Only 5% of Babies Arrive on Their Due Date
The due date is an estimate, not a promise. About 90% of babies arrive within 2 weeks of the due date (up to 2 weeks before or 2 weeks after). Your baby comes when your body and baby are ready.
•
Ultrasound May Refine Your Estimate
An ultrasound in the first trimester can be more accurate than an LMP-based calculation. Second trimester ultrasounds are less accurate, and third trimester ultrasounds are least accurate. Your doctor will use all available information to narrow down your due date.
•
Twins and Multiples Have Different Timelines
If you're carrying multiples (twins, triplets, etc.), you'll likely deliver earlier than 40 weeks. Twins typically arrive around week 36-37. Your doctor will give you specific guidance based on your situation.
•
IVF Dates Are Calculated Differently
If you conceived through IVF, your due date is calculated differently because we know the exact fertilization date. Talk to your fertility specialist about your specific due date, as it may differ from standard LMP calculations.
•
Your Doctor's Estimate Takes Priority
Use this calculator for a general idea, but your healthcare provider's estimate based on your exams and ultrasounds is the official due date. Always confirm your due date with your doctor at your first prenatal visit.
•
Early Labor and Induction Dates Matter
Hospitals often schedule induction or planned c-sections around 39 weeks. You might deliver before your due date for medical reasons. This is normal and safe when medically necessary.

Signs of Each Trimester

Every pregnancy is unique, but here are common signs and changes for each trimester:

First Trimester Symptoms

▪ Nausea and morning sickness
▪ Extreme fatigue and tiredness
▪ Breast tenderness and swelling
▪ Food cravings and aversions
▪ Mood swings and emotions
▪ Frequent urination
▪ Headaches and dizziness
▪ Bloating and gas

Second Trimester Changes

▪ Energy returning and feeling better
▪ Visible belly showing
▪ Baby movements felt (quickening)
▪ Skin changes (glow or darkening)
▪ Appetite increase
▪ Hair and nail growth acceleration
▪ Occasional back pain
▪ Nasal congestion and nosebleeds

Third Trimester Effects

▪ Increased heaviness and fatigue
▪ Lower back and pelvic pain
▪ Frequent urination and constipation
▪ Difficulty sleeping and insomnia
▪ Braxton-Hicks contractions
▪ Shortness of breath
▪ Swelling in ankles and feet
▪ Excitement and anxiety about birth

Questions to Ask Your Doctor

During your prenatal visits, don't hesitate to ask your healthcare provider these important questions:

Q
"What is my exact due date based on your examination?"
Get your doctor's official due date, not just your calculated one. Confirm it at your first visit and again after your first ultrasound.
Q
"What tests and screenings will I have during each trimester?"
Understand the testing schedule: glucose test, group B strep test, ultrasounds, and any other screenings. Know what they check and when.
Q
"What nutritional changes should I make during pregnancy?"
Ask about prenatal vitamins, foods to avoid, safe weight gain, and any dietary restrictions specific to your situation.
Q
"Is exercise safe during my pregnancy, and what should I do?"
Most pregnancies benefit from gentle exercise, but ask your doctor what's safe for you specifically. Get clearance before starting any new routines.
Q
"What warning signs should I watch for at home?"
Know the red flags that require immediate medical attention: heavy bleeding, severe pain, signs of labor before due date, or decreased baby movement.
Q
"What are my labor and delivery options?"
Discuss birth preferences, pain management options, hospital policies, and who can be present during delivery.
Q
"Should I take any medications or supplements?"
Some medications are safe in pregnancy, others aren't. Always confirm with your doctor before taking anything, including over-the-counter drugs.
Q
"How will we monitor my baby's growth and health?"
Understand how your doctor tracks your baby's development, what measurements matter, and what to do if something looks off.

Frequently Asked Questions

How accurate is the due date from LMP? +

The LMP-based due date is accurate within plus or minus 2 weeks for about 95% of pregnancies. That means your due date could be 2 weeks earlier or 2 weeks later than calculated, and still be completely normal. An ultrasound in the first trimester can narrow this down to plus or minus 3 to 5 days, making it even more accurate. The earlier you get an ultrasound, the more precise your due date becomes. This is why your doctor will often refine your due date after seeing your baby on the scan.

What if my periods are irregular? +

If you have irregular periods, the LMP method becomes less reliable because we can't know for certain exactly when ovulation happened. This is why an ultrasound is even more important for you. A first trimester ultrasound can pinpoint your baby's age much more accurately than the LMP date. Tell your doctor about your irregular cycle at your first visit. They'll rely more heavily on ultrasound measurements to establish your due date. If you have a very long cycle, your due date might be adjusted later than the standard 280 days.

When should I tell people I'm pregnant? +

There's no perfect time to announce your pregnancy. Many women wait until after the first trimester (after week 12-13) because the risk of miscarriage drops significantly after this point. This is sometimes called "telling after the first trimester rule." However, the choice is entirely yours. Some women tell immediately, others wait until showing. Tell your employer when you're ready. There's no medical requirement to tell anyone before you feel comfortable. Consider your own comfort level, your work situation, and your preferences. Some women tell immediate family immediately but wait to announce publicly.

What is the difference between gestational age and fetal age? +

Gestational age is counted from the first day of your last menstrual period. This is what doctors use because it's easy to track. Fetal age (also called fertilization age or conception age) is counted from the day sperm and egg actually met. Conception usually happens about 2 weeks after your LMP. So when doctors say you're 8 weeks pregnant, that's gestational age. Your baby is actually about 6 weeks old in terms of fetal development. This two-week difference can be confusing, but your doctor will explain which age they're referring to. Always use gestational age when talking with your healthcare provider to avoid confusion.

Can the due date change after an ultrasound? +

Yes, your due date can change after an ultrasound, especially early in pregnancy. A first trimester ultrasound might show your baby is larger or smaller than the LMP calculation suggested, moving your due date earlier or later by a few days. This is normal and actually helpful. Second trimester ultrasounds occasionally adjust the date slightly. By the third trimester, ultrasound measurements are less accurate for dating, so your doctor usually sticks with the earlier due date unless there's a significant difference. Always ask your doctor if your due date changes and why. Multiple ultrasounds throughout pregnancy give the clearest picture of your baby's growth and due date.

What week is considered full-term? +

Full-term is defined as 39 weeks of pregnancy or later. Babies born at 39 weeks have the lowest risk of complications from prematurity. Weeks 37 and 38 are considered "early term," meaning delivery is safe but they still have slightly higher risks than full-term babies. Before 37 weeks is considered preterm, which carries additional medical considerations. Most hospitals prefer waiting until at least 39 weeks for scheduled deliveries unless there's a medical reason for earlier delivery. If you go into labor naturally before 39 weeks, that's fine. Most babies born between 37 and 42 weeks do perfectly fine. Your doctor will discuss timing with you based on your specific situation.

Pregnancy Details