Pregnancy Calculator
Due date, trimester timeline, weekly milestones & key dates| Week | Date | Baby Development |
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Our Pregnancy Calculator tells you exactly how far along you are, your estimated due date, current trimester, and a complete week-by-week pregnancy timeline — all in seconds. Enter your Last Menstrual Period (LMP), conception date, due date, ultrasound date, or IVF transfer date to get your personalized results instantly.
How Many Weeks Pregnant Am I? — 5 Ways to Calculate
Not sure which method to use? Here are the five most accurate ways to calculate your pregnancy weeks:
1. Last Menstrual Period (LMP) Method — The most widely used clinical method. Enter the first day of your last period and your average cycle length. The calculator adds 280 days (40 weeks) to give your estimated due date. Works best for women with regular 28-day cycles.
2. Due Date Method — Already know your due date? Work backwards. The calculator counts from today to your due date to tell you exactly how many weeks and days pregnant you are right now.
3. Conception Date Method — If you know the exact date you conceived, enter it here. The tool adds 266 days (38 weeks) from conception to estimate your delivery date.
4. Ultrasound Dating Method — Enter your ultrasound scan date and the gestational age shown on the scan. Ultrasound dating, especially before 13 weeks, is the most accurate way to determine how far along you are — particularly if your cycle is irregular.
5. IVF Transfer Date Method — If you conceived through in vitro fertilization, enter your embryo transfer date and select either a Day 3 or Day 5 transfer. IVF pregnancy dating is the most precise of all methods since the exact moment of fertilization is known.
What Does This Pregnancy Calculator Tell You?
Once you hit Calculate, you instantly get:
- Your current pregnancy week and day — for example, “You are 14 weeks and 3 days pregnant”
- Your estimated due date (EDD) — when your baby is likely to arrive
- Your current trimester — First, Second, or Third
- Trimester breakdown with exact start and end dates
- Your estimated conception date
- How many months pregnant you are
- Days remaining until your due date
- Key pregnancy milestones week by week
How Is Pregnancy Calculated? Why Does It Start From Your Last Period?
This is one of the most common questions pregnant women ask — and the answer surprises many people.
Pregnancy is officially counted from the first day of your last menstrual period (LMP), not the day you actually conceived. This may seem strange, but there is a solid medical reason behind it.
Conception typically happens around Day 14 of a 28-day cycle — about two weeks after your period starts. But because the exact moment of conception is nearly impossible to pinpoint for most women (sperm can survive up to 5 days in the reproductive tract, and ovulation timing varies), doctors use the first day of your last period as a fixed, reliable reference point.
This means that when your doctor says you are “4 weeks pregnant,” your baby has actually been developing for only about 2 weeks since conception. The extra 2 weeks at the beginning are counted as part of your cycle before conception occurred.
Naegele’s Rule — the formula developed by German obstetrician Franz Naegele in 1812 and still used worldwide today — calculates your due date by taking the first day of your LMP, adding one year, subtracting three months, and adding seven days. In simpler terms: LMP + 280 days = Estimated Due Date (EDD).
Pregnancy Weeks to Months Chart — How Many Months Am I?
Many women think of pregnancy in months, but doctors track it in weeks. Here is the complete pregnancy weeks-to-months conversion:
| Weeks Pregnant | Months Pregnant | Trimester |
|---|---|---|
| 1 – 4 weeks | 1 month | First Trimester |
| 5 – 8 weeks | 2 months | First Trimester |
| 9 – 13 weeks | 3 months | First Trimester |
| 14 – 17 weeks | 4 months | Second Trimester |
| 18 – 21 weeks | 5 months | Second Trimester |
| 22 – 26 weeks | 6 months | Second Trimester |
| 27 – 30 weeks | 7 months | Third Trimester |
| 31 – 35 weeks | 8 months | Third Trimester |
| 36 – 40 weeks | 9 months | Third Trimester |
A full-term pregnancy is considered 37 to 42 weeks, as defined by the World Health Organization. Babies born between these weeks are considered full-term and ready for birth.
Three Trimesters of Pregnancy — What to Expect Week by Week
First Trimester (Weeks 1–13) — The Foundation
The first trimester runs from Week 1 through Week 13 (approximately 3 months). This is when the most dramatic early development happens.
- Week 4–5: Pregnancy hormone hCG becomes detectable — this is when most home pregnancy tests turn positive
- Week 6–8: Baby’s heartbeat begins; major organs start forming
- Week 10–13: First trimester screening (nuchal translucency ultrasound + blood test) is scheduled
- Week 13: End of first trimester — risk of miscarriage drops significantly
Key symptoms: nausea (morning sickness), breast tenderness, fatigue, frequent urination, heightened sense of smell.
Second Trimester (Weeks 14–26) — The Sweet Spot
Most women feel best during the second trimester. Energy returns, morning sickness usually fades, and the baby bump becomes visible.
- Week 18–22: Anatomy scan ultrasound — detailed examination of baby’s organs, brain, heart, and limbs. You may also find out the baby’s sex.
- Week 20: Halfway point of your pregnancy
- Week 24: Viability milestone — a baby born at this point has a chance of survival with intensive neonatal care
Key symptoms: visible baby bump, feeling baby’s first movements (quickening), back pain, round ligament pain.
Third Trimester (Weeks 27–40) — The Home Stretch
The final trimester is when your baby gains most of its weight and prepares for birth.
- Week 28: Third trimester begins; regular prenatal visits increase in frequency
- Week 32–36: Baby’s position monitored; Group B Strep test scheduled
- Week 37: Baby is considered “early term” — fully developed and safe to deliver
- Week 40: Your estimated due date (EDD)
- Week 42: Post-term pregnancy — induction typically discussed
Key symptoms: difficulty sleeping, frequent urination, Braxton Hicks contractions, swollen feet and ankles, shortness of breath.
How Accurate Is a Pregnancy Due Date?
Here is the most important thing to understand about your estimated due date: it is an estimate, not a deadline.
Only about 4–5% of babies are born on their exact due date. Research shows that roughly 60% of births happen within one week of the due date, and close to 90% occur within two weeks on either side. The actual length of your pregnancy depends on factors like your age, your cycle length, your weight, and the baby’s growth pattern — many of which are still not fully predictable even with modern medicine.
The most accurate way to confirm your due date is a first-trimester ultrasound performed before 13 weeks. At this stage, all babies grow at roughly the same rate, so measurements of the baby’s crown-rump length (CRL) give a very precise gestational age. After 13 weeks, individual growth variation increases and ultrasound dating becomes slightly less reliable.
If there is a difference of more than 5–7 days between your LMP-based date and your ultrasound date, your doctor may adjust your official due date to match the ultrasound findings.
IVF Pregnancy Calculator — Week-by-Week Dating for IVF Pregnancies
If you conceived through IVF, calculating your pregnancy weeks works slightly differently. Since the exact date of fertilization is known, IVF dating is actually more precise than natural conception dating.
For a Day 5 embryo transfer: Subtract 19 days from your transfer date to find your LMP equivalent. Add 40 weeks from that point for your estimated due date.
For a Day 3 embryo transfer: Subtract 17 days from your transfer date to find your LMP equivalent, then add 40 weeks.
Our IVF Pregnancy Calculator handles all of this automatically — just select “IVF Transfer Date,” enter the transfer date, and choose Day 3 or Day 5. Your pregnancy week, trimester, and due date are calculated instantly.
Pregnancy Detection — When Can You Take a Pregnancy Test?
Wondering if you are pregnant? Here is what the science says about timing your test.
Home urine pregnancy tests detect the hormone human chorionic gonadotropin (hCG), which is only present during pregnancy. hCG levels are detectable in urine as early as 10–14 days after fertilization — which is typically around the time of your missed period. Taking a test too early (before hCG builds up enough) may give a false negative even if you are pregnant.
Clinical blood tests can detect hCG even earlier — 6 to 8 days after fertilization — and can measure the exact amount of hCG in your blood, which is useful for monitoring early pregnancy health.
Signs that suggest you may be pregnant (before testing):
- Missed menstrual period
- Elevated basal body temperature
- Unusual fatigue or tiredness
- Nausea or vomiting (morning sickness)
- Breast soreness or tenderness
- More frequent urination than usual
- Light spotting or implantation bleeding
Pregnancy Milestones Timeline — Key Dates to Know
| Milestone | Typical Timing |
|---|---|
| Positive pregnancy test | 4–5 weeks |
| First prenatal appointment | 6–8 weeks |
| Heartbeat detected on ultrasound | 6–7 weeks |
| End of first trimester | 13 weeks |
| First-trimester screening window | 11–14 weeks |
| Start of second trimester | 14 weeks |
| Anatomy scan ultrasound | 18–22 weeks |
| Halfway point | 20 weeks |
| Viability milestone | 24 weeks |
| Third trimester begins | 27–28 weeks |
| Baby considered early term | 37 weeks |
| Estimated due date | 40 weeks |
| Post-term pregnancy | 42 weeks |
Pregnancy Management — What to Keep in Mind Each Trimester
Medications During Pregnancy
Always consult your doctor before taking any medication during pregnancy. In the U.S., the FDA classifies drugs from Category A (safest, proven safe for the fetus) to Category X (proven fetal risks that outweigh any benefit). Never self-medicate during pregnancy without professional guidance.
Weight Gain Guidelines
Healthy weight gain during pregnancy is important for both mother and baby. The Institute of Medicine recommendations based on pre-pregnancy BMI are:
- Underweight (BMI under 18.5): 28–40 pounds recommended
- Normal weight (BMI 18.5–24.9): 25–35 pounds recommended
- Overweight (BMI 25–29.9): 15–25 pounds recommended
- Obese (BMI 30+): 11–20 pounds recommended
Both insufficient and excessive weight gain can increase risks for both mother and baby, including gestational hypertension and the need for cesarean section.
Exercise During Pregnancy
Regular moderate exercise is beneficial during an uncomplicated pregnancy. The American College of Obstetricians and Gynecologists confirms that fetal injuries from exercise are unlikely in healthy pregnancies. However, contact your doctor immediately if you experience vaginal bleeding, dizziness, chest pain, decreased fetal movement, or preterm contractions while exercising.
Nutrition and Prenatal Vitamins
Pregnancy requires higher amounts of specific nutrients than a non-pregnant state. Most critical:
- Folic acid (Vitamin B9): Reduces the risk of neural tube defects. Start before conception ideally.
- DHA Omega-3: Essential for baby’s brain and retinal development — must be obtained through diet or supplements since the baby cannot produce it.
- Iron: Supports increased blood volume and prevents anemia.
- Calcium: Critical for baby’s bone development.
Always consult your doctor or registered dietitian for a personalized prenatal nutrition plan.
Frequently Asked Questions About Pregnancy Weeks & Due Dates
How do I know how many weeks pregnant I am?
Enter the first day of your last menstrual period into our pregnancy calculator. It will instantly tell you your current week and day of pregnancy.
How many weeks is a full-term pregnancy?
A full-term pregnancy is between 37 and 42 weeks, as defined by the World Health Organization. Most pregnancies last 40 weeks from the LMP.
How many weeks is 9 months pregnant?
Nine months of pregnancy equals approximately 36 to 40 weeks. Because pregnancy months do not align perfectly with calendar months, tracking in weeks is more accurate.
What week does the second trimester start?
The second trimester begins at Week 14 and ends at Week 26.
What week does the third trimester start?
The third trimester begins at Week 27 (some providers say Week 28) and continues through Week 40 and beyond.
How many months is 12 weeks pregnant?
12 weeks pregnant is approximately 3 months into your pregnancy, and it marks the end of the first trimester.
How many months is 20 weeks pregnant?
20 weeks pregnant is 5 months — and it is the halfway point of your pregnancy.
How many months is 28 weeks pregnant?
28 weeks pregnant is approximately 7 months and marks the beginning of the third trimester.
How many weeks is 6 months pregnant?
Six months pregnant is approximately 22 to 26 weeks.
Can my due date change after it is calculated?
Yes. If an early ultrasound shows a significant difference (more than 5–7 days) from your LMP-based due date, your healthcare provider may adjust your official due date based on the ultrasound measurement. Due dates are rarely changed more than once.
Why is pregnancy calculated from the last period and not conception?
Because the exact day of conception is difficult to determine for most women. The first day of your last period is a consistent, reliably remembered reference point that doctors worldwide use as the starting date for all pregnancy calculations.
How many weeks does a pregnancy last?
A typical pregnancy lasts 40 weeks from the first day of the last menstrual period, though healthy births can occur anywhere between 37 and 42 weeks.
What is Naegele’s Rule?
Naegele’s Rule is the standard formula for calculating estimated due dates. It adds 280 days (40 weeks) to the first day of your last menstrual period. It was established by German obstetrician Franz Naegele in 1812 and remains the global standard today.
Pregnancy Calendar — Your Week-by-Week Journey at a Glance
Tracking your pregnancy week by week helps you stay informed and prepared at every stage. From the first flutter of nausea in Week 6 to the excitement of your anatomy scan at Week 20, to the final countdown in Week 38 and 39 — each week brings new milestones for both you and your growing baby.
Use our Pregnancy Week Calculator alongside your prenatal appointments to stay on top of every stage. Whether you are calculating from your last period, your due date, your conception date, or your IVF transfer date — this tool gives you a clear, accurate pregnancy timeline customized to your journey.
Track your pregnancy confidently. Every week matters.