Pregnancy Week Calculator – How Far Along Am I?

How Pregnancy Weeks Are Counted

Pregnancy is measured in weeks from the first day of the last menstrual period (LMP), not from conception. This means at conception (typically week 2–3), you're already 2–3 weeks pregnant by medical counting. Full-term pregnancy is 40 weeks, but term is broadly defined as 37–42 weeks.

Week-by-week pregnancy counting gives precise gestational age, used to track fetal development, schedule screenings, and determine delivery timing. Knowing your gestational week helps you understand expected fetal size, appropriate prenatal tests, and normal symptom timelines.

Fetal Development by Trimester

A summary of key developmental milestones by gestational week:

Prenatal Screenings by Week

Prenatal care follows a schedule based on gestational weeks:

• Weeks 10–13: First trimester screening (nuchal translucency ultrasound + blood test for chromosomal abnormalities including Down syndrome)
• Weeks 15–20: Optional quad screen/MSAFP blood test for neural tube defects and chromosomal issues
• Weeks 18–20: Anatomy ultrasound — detailed structural scan of fetus
• Week 24–28: Gestational diabetes screening (glucose tolerance test)
• Weeks 35–37: Group B Streptococcus (GBS) swab; delivery planning discussions
• Week 40+: Biophysical profiles, non-stress tests if going post-dates

Common Symptoms by Trimester

Understanding what symptoms are normal at each stage helps distinguish typical pregnancy changes from concerns requiring medical attention:

• First trimester (weeks 1–12): Nausea/vomiting (70% of women), fatigue, breast tenderness, frequent urination, food aversions. Mild spotting (implantation bleeding) may occur around week 4. Heavy bleeding requires immediate evaluation.
• Second trimester (weeks 13–26): Nausea typically subsides; energy improves. Round ligament pain (sharp brief pain from uterine ligaments) is common. Fetal movement (quickening) begins around weeks 16–20 for first-time mothers.
• Third trimester (weeks 27–40): Back pain from weight distribution changes, heartburn from uterine pressure on stomach, Braxton-Hicks contractions, shortness of breath, edema (swelling in feet/ankles), frequent urination returns.

Running Through Pregnancy: Week-by-Week Guide

Many runners continue training through significant portions of pregnancy. Here's a general week-by-week guide for previously active runners:

• Weeks 1–12: Can generally maintain pre-pregnancy intensity if nausea and fatigue permit. Many women run normally through the first trimester. Heart rate limits (140 bpm or 'can hold a conversation') are outdated — current guidelines focus on perceived exertion (5–7/10).
• Weeks 13–20: Continue running with pace reduction as needed. Center of gravity shifts; consider trail shoes or extra cushioning on roads. Hydration is critical — pregnant women dehydrate faster.
• Weeks 21–28: Running becomes increasingly uncomfortable for many. Pelvic girdle pain, Braxton-Hicks contractions, or simply discomfort may signal transition to walking or water running.
• Weeks 28–40: Most runners have transitioned to walking, swimming, or stationary cycling. Stop running if contractions increase or pelvic pressure is uncomfortable.

Calculating Your Current Pregnancy Week

To find your current gestational week: count the days from the first day of your last menstrual period to today, then divide by 7. Example: LMP was 10 weeks and 3 days ago → you're in week 10 day 3 of pregnancy.

Week 1, day 1 = the first day of your LMP. Each week starts on the same day of the week as your LMP. If your LMP was on a Wednesday, each new gestational week begins on Wednesday. Our calculator computes this automatically from your LMP date and today's date, providing your exact gestational week and day along with developmental milestones.

Tips for Getting Accurate Results

For the most accurate calculations, use precise inputs. Body weight should be measured at the same time each day (morning, after using the bathroom, before eating). Height should be measured standing straight against a wall. For calculations involving body fat percentage, use consistent measurement methods — if using bioelectrical impedance scales, measure at the same hydration level each time. If tracking changes over time, compare measurements taken under identical conditions.

Remember that all calculators provide estimates based on population averages and validated formulas. Individual variation is real — genetic factors, hormonal status, training history, and gut microbiome composition all affect how your body responds to diet and exercise. Use calculator outputs as starting points and adjust based on your real-world results over 4–8 weeks.

When to Consult a Healthcare Professional

These calculators are educational tools for general health and fitness guidance. They are not medical devices and do not replace professional medical advice. Consult a healthcare professional if: your results indicate values outside healthy ranges (BMI under 17 or over 35, body fat under 5% for men or 10% for women); you're experiencing symptoms that concern you; you're pregnant, have a chronic medical condition, or take medications that affect metabolism; or you're planning significant dietary or exercise changes alongside a medical condition.

For personalized nutrition advice, a registered dietitian (RD/RDN) can provide individualized guidance based on your complete health picture. For performance optimization, a sports medicine physician or certified strength and conditioning specialist (CSCS) can assess your fitness and create appropriate programming.

Nutrition by Trimester: What to Eat When

Nutritional needs shift significantly across pregnancy. The American College of Obstetricians and Gynecologists (ACOG) and WHO provide evidence-based guidelines for each trimester:

Key foods to prioritize: leafy greens and legumes (folate), lean red meat or fortified cereals (iron), dairy or fortified alternatives (calcium), fatty fish like salmon twice weekly (DHA and vitamin D). Foods to avoid: raw fish, unpasteurized cheeses, deli meats (listeria risk), high-mercury fish (shark, swordfish, king mackerel), and alcohol in any amount. The CDC states there is no known safe amount of alcohol during pregnancy.

Weight Gain During Pregnancy: What's Normal

Healthy weight gain during pregnancy depends on pre-pregnancy BMI. The Institute of Medicine (IOM) 2009 guidelines, endorsed by ACOG, recommend:

Where does the weight go? By 40 weeks: baby ~3.4 kg, placenta ~0.7 kg, amniotic fluid ~0.8 kg, uterus ~0.9 kg, breast tissue ~0.5 kg, blood volume increase ~1.4 kg, fluid retention ~1.4 kg, maternal fat stores ~2.7–3.6 kg. Understanding this breakdown helps contextualize weight gain as mostly physiologically necessary rather than "extra fat."

For active runners: maintain a consistent exercise routine during pregnancy (as cleared by your provider) to support healthy weight gain within these ranges. Research published in Obstetrics & Gynecology shows that regular exercise during pregnancy reduces the risk of excessive gestational weight gain by 30–40%.

Due Date Calculation Methods Compared

Multiple methods exist for estimating the due date (estimated date of delivery, or EDD). Understanding their accuracy helps manage expectations — only about 5% of babies arrive on their exact due date:

• Naegele's Rule (LMP-based): Add 280 days (40 weeks) to the first day of the LMP. This is the standard method used by our calculator and most healthcare providers. Assumption: 28-day cycle with ovulation on day 14. Accuracy: ±2 weeks for women with regular 28-day cycles.
• First-trimester ultrasound (crown-rump length): Measured at weeks 8–13, this is the most accurate dating method, with accuracy of ±3–5 days. If ultrasound dating differs from LMP dating by more than 7 days, ultrasound dates are used.
• Known conception date: If you know the exact date of conception (IVF, tracked ovulation), add 266 days. More accurate than LMP for women with irregular cycles.
• Mittendorf-Williams Rule: A refinement of Naegele's that accounts for cycle length variation: for first pregnancies, add 288 days to LMP; for subsequent pregnancies, add 283 days. Slightly more accurate for non-standard cycle lengths.

Important: the "due date" is an estimate of the middle of a normal delivery window. Full-term delivery anywhere between 37 and 42 weeks is normal. According to the British Medical Journal, the median delivery date for first-time mothers is actually 41 weeks and 1 day — 8 days after the standard "due date."