🤰 Pregnancy Due Date Calculator

How Naegele's Rule Works

Our pregnancy calculator uses Naegele's Rule, the standard method used by obstetricians and midwives worldwide to estimate your expected due date (EDD). Named after German obstetrician Franz Karl Naegele who popularized it in the early 1800s, the calculation adds 280 days (40 weeks) to the first day of your last menstrual period (LMP). This 280-day figure accounts for the average 14-day gap between the start of menstruation and ovulation in a standard 28-day cycle, plus 266 days of actual gestational development from conception to birth.

Our calculator also lets you enter your actual cycle length. If your cycles are longer or shorter than 28 days, the due date adjusts accordingly. For example, if your cycle is 35 days, ovulation likely occurs around day 21 rather than day 14, so your due date shifts 7 days later. This personalization makes the estimate more accurate than the basic formula alone. Keep in mind that only about 5% of babies are born on their exact due date. Most deliveries occur within a window of 37 to 42 weeks, which is considered full term.

Understanding the Three Trimesters

First Trimester (Weeks 1-12)

The first trimester is the most critical period of fetal development. During these 12 weeks, a fertilized egg transforms from a microscopic cluster of cells into a recognizable human form with all major organs beginning to develop. The heart starts beating around week 6, and by week 12 the fetus is about 2.5 inches long and weighs roughly half an ounce. Many women experience morning sickness (affecting 70-80% of pregnancies), fatigue, breast tenderness, and frequent urination during this period. The risk of miscarriage is highest in the first trimester, dropping significantly after a healthy heartbeat is confirmed at the 8-week mark.

Second Trimester (Weeks 13-26)

Often called the honeymoon phase of pregnancy, the second trimester typically brings relief from first-trimester symptoms. Energy returns, nausea subsides, and the growing bump becomes visible. Around week 18 to 22, most women feel the first fetal movements, known as quickening. The anatomy scan ultrasound at 18-22 weeks provides a detailed look at the baby's development and can reveal the sex. By the end of the second trimester, the baby weighs about 1.5 pounds and is approximately 13 inches long. The baby can hear sounds, respond to light, and has developed fingerprints.

Third Trimester (Weeks 27-40)

The final stretch is characterized by rapid fetal growth and weight gain. The baby's lungs mature, fat stores develop for temperature regulation after birth, and the brain undergoes enormous growth. Common maternal symptoms include heartburn, back pain, swollen ankles, shortness of breath, and difficulty sleeping. Braxton Hicks contractions (practice contractions) become more frequent. Around week 36, the baby typically settles into a head-down position in preparation for delivery. At 40 weeks, the average baby weighs 7 to 8 pounds and measures about 20 inches long.

Prenatal Care Schedule (ACOG Recommendations)

The American College of Obstetricians and Gynecologists (ACOG) recommends a specific schedule of prenatal visits for healthy, uncomplicated pregnancies:

• First visit (6-8 weeks): Comprehensive health history, physical exam, blood work (blood type, Rh factor, CBC, HIV, hepatitis B and C, rubella immunity, syphilis, STI screening), urinalysis, and often an early ultrasound to confirm viability and dating.
• Monthly visits (through week 28): Typically scheduled every 4 weeks. Each visit includes weight check, blood pressure measurement, urine test for protein and glucose, fundal height measurement, and fetal heart rate check with a Doppler device.
• Biweekly visits (weeks 28-36): Every 2 weeks to monitor for signs of preeclampsia, gestational diabetes management, and fetal growth.
• Weekly visits (weeks 36-40): Weekly appointments that may include cervical checks, Group B Strep screening (around week 36), and non-stress tests if indicated.

High-risk pregnancies (including those involving advanced maternal age, multiples, gestational diabetes, or preeclampsia) require more frequent monitoring. Most insurance plans, including Medicaid and plans under the Affordable Care Act, cover prenatal visits at no out-of-pocket cost.

Important Prenatal Screenings and Tests

Throughout pregnancy, several screenings are offered to assess the health of both mother and baby:

• NT Scan + First Trimester Screening (11-14 weeks): Combines a blood test measuring PAPP-A and hCG levels with an ultrasound measuring the nuchal translucency (the fluid at the back of the baby's neck). Detects approximately 85-90% of Down syndrome cases.
• Cell-Free DNA (NIPT) Screening (after 10 weeks): A blood test analyzing fetal DNA fragments in the mother's blood. Over 99% detection rate for trisomy 21 (Down syndrome), trisomy 18, and trisomy 13. Increasingly offered as a standard option, though not always covered by insurance.
• Anatomy Scan (18-22 weeks): A detailed ultrasound examining the baby's brain, heart, spine, kidneys, limbs, and other organs. Also checks placental position and amniotic fluid levels.
• Glucose Tolerance Test (24-28 weeks): Screens for gestational diabetes, which affects 6-9% of pregnancies in the United States. The initial one-hour test involves drinking a glucose solution and having blood drawn after one hour. If the result is elevated, a three-hour test follows.
• Group B Strep (GBS) Test (35-37 weeks): A vaginal and rectal swab to check for GBS bacteria. If positive (approximately 25% of women carry GBS), IV antibiotics are administered during labor to prevent transmission to the baby.

Nutrition During Pregnancy

Proper nutrition is critical for a healthy pregnancy. The following nutrients deserve special attention:

• Folic Acid: 400-800 micrograms daily, ideally starting at least one month before conception and continuing through the first trimester. Reduces the risk of neural tube defects (such as spina bifida) by up to 70%. Found in leafy greens, fortified cereals, beans, and prenatal vitamins.
• Iron: 27 mg daily during pregnancy (nearly double the non-pregnant requirement). Essential for making additional blood to supply oxygen to the baby. Iron deficiency anemia affects up to 18% of pregnant women in the US. Lean red meat, beans, spinach, and fortified cereals are good sources. Pair with vitamin C to enhance absorption.
• Calcium: 1,000 mg daily for bone development. Dairy products, fortified plant milks, broccoli, and almonds are excellent sources.
• DHA Omega-3: 200-300 mg daily for fetal brain and eye development. Found in fatty fish like salmon and sardines (limit to 2-3 servings per week), or available as a supplement.
• Caloric needs: No additional calories are needed in the first trimester. Add approximately 340 extra calories per day in the second trimester and 450 in the third trimester.

Foods to avoid include raw or undercooked meat and seafood, unpasteurized dairy products, high-mercury fish (swordfish, king mackerel, shark, tilefish), deli meats unless heated until steaming, raw sprouts, and alcohol (no amount is considered safe during pregnancy).

Signs of Labor and When to Call Your Provider

Recognizing the signs of labor is essential as your due date approaches. The main indicators include:

• Regular contractions: True labor contractions become progressively stronger, longer, and closer together. The general guideline is the 5-1-1 rule: contractions every 5 minutes, lasting 1 minute each, for at least 1 hour. At this point, contact your provider or head to the hospital.
• Water breaking: A gush or steady trickle of clear, odorless fluid indicates the amniotic sac has ruptured. Go to the hospital promptly, as delivery should occur within 24 hours to reduce infection risk.
• Bloody show: A pink or blood-tinged mucus discharge indicating the cervix is dilating. This can occur hours to days before active labor begins.
• Back labor: Intense, persistent lower back pain that comes in waves, sometimes with little abdominal pain. This occurs when the baby is facing the mother's abdomen (posterior position).

Contact your provider immediately if you experience heavy vaginal bleeding, severe headaches with vision changes, sudden swelling of the face or hands (possible signs of preeclampsia), or a significant decrease in fetal movement. Most hospitals recommend that first-time mothers come in when contractions follow the 5-1-1 pattern, while women who have given birth before may be advised to come sooner as labor often progresses faster with subsequent pregnancies.

Maternity Leave in the United States

Unlike most developed nations, the United States has no federal paid maternity leave law. The Family and Medical Leave Act (FMLA) provides eligible employees with up to 12 weeks of unpaid, job-protected leave for the birth or adoption of a child. To qualify, you must work for an employer with 50 or more employees, have worked there for at least 12 months, and have logged at least 1,250 hours in the past year. FMLA covers both mothers and fathers.

However, paid leave varies significantly by employer and state. As of 2026, the following states and Washington D.C. have enacted paid family leave programs: California (up to 8 weeks at 60-70% pay), New York (up to 12 weeks at 67%), New Jersey (up to 12 weeks at 85%), Washington (up to 12 weeks at 90%), Massachusetts (up to 12 weeks at 80%), Connecticut, Oregon, Colorado, Maryland, Delaware, Minnesota, Maine, and the District of Columbia. Many employers also offer paid parental leave as a benefit, ranging from 2 weeks to 6 months depending on the company.

Short-term disability insurance, if purchased before conception, can also provide partial income replacement during the recovery period after birth (typically 6 weeks for vaginal delivery, 8 weeks for cesarean). Planning for the financial impact of maternity leave is an important step during pregnancy.

Weight Gain Recommendations During Pregnancy

The Institute of Medicine (now the National Academy of Medicine) provides the following guidelines for total weight gain during a singleton pregnancy based on pre-pregnancy BMI:

• Underweight (BMI below 18.5): 28 to 40 pounds total gain recommended.
• Normal weight (BMI 18.5-24.9): 25 to 35 pounds.
• Overweight (BMI 25-29.9): 15 to 25 pounds.
• Obese (BMI 30 and above): 11 to 20 pounds.

Weight gain is minimal during the first trimester (approximately 1 to 4 pounds total). During the second and third trimesters, steady gain of about 1 pound per week is typical for normal-weight women. This weight comprises the baby (7-8 pounds at birth), the placenta (1-2 pounds), amniotic fluid (2 pounds), increased blood volume (3-4 pounds), enlarged uterus (2 pounds), breast tissue (1-3 pounds), and maternal fat stores (5-9 pounds). Excessive weight gain increases the risk of gestational diabetes, preeclampsia, and cesarean delivery, while insufficient gain can lead to preterm birth and low birth weight.