Pregnancy Calculator
Enter the first day of your last menstrual period or the due date, and you'll see the pregnancy week, trimester, and important dates.
Key milestones
Pregnancy Calculator — Due Date and Weekly Tracker
The pregnancy calculator estimates your due date, current pregnancy week, and trimester based on the first day of your last menstrual period (LMP). It also highlights important milestone dates such as ultrasound windows and the start of each trimester.
How Are Pregnancy Weeks Calculated?
Pregnancy is dated from the first day of the last menstrual period (LMP), not from the date of conception. Because ovulation typically occurs about two weeks after LMP, the first two "weeks" of pregnancy actually occur before the egg is fertilized. The estimated due date (EDD) is 40 weeks (280 days) from the LMP.
Due Date = LMP + 280 days
This method is known as Naegele's Rule, named after the German obstetrician who popularized it in the early 1800s. An alternative formula, the Mittendorf-Williams rule, adjusts for first pregnancies (which tend to run slightly longer) and other factors.
Pregnancy Trimesters
| Trimester | Weeks | Key Developments |
|---|---|---|
| 1st trimester | Weeks 1 – 12 | Implantation, heartbeat begins (week 6), morning sickness common, all major organs form |
| 2nd trimester | Weeks 13 – 27 | Baby kicks felt (weeks 18–22), gender visible on ultrasound, rapid growth |
| 3rd trimester | Weeks 28 – 40 | Lungs mature, baby gains weight, nesting instinct, preparation for birth |
Week-by-Week Size Comparison
| Week | Baby Size | Comparable To | Weight |
|---|---|---|---|
| 8 | 0.6 in (1.6 cm) | Raspberry | ~0.04 oz |
| 12 | 2.1 in (5.4 cm) | Lime | ~0.5 oz |
| 16 | 4.6 in (11.6 cm) | Avocado | ~3.5 oz |
| 20 | 6.5 in (16.4 cm) | Banana | ~10 oz |
| 24 | 11.8 in (30 cm) | Ear of corn | ~1.3 lbs |
| 28 | 14.8 in (37.6 cm) | Eggplant | ~2.2 lbs |
| 32 | 16.7 in (42.4 cm) | Squash | ~3.75 lbs |
| 36 | 18.7 in (47.4 cm) | Honeydew melon | ~5.8 lbs |
| 40 | 20.2 in (51.2 cm) | Watermelon | ~7.5 lbs |
Important Prenatal Appointments
- First prenatal visit (weeks 8–10) — Confirms pregnancy, estimates due date, orders blood work, reviews medical history
- Dating ultrasound (weeks 11–14) — Measures fetal size, checks nuchal translucency for chromosomal screening
- Anatomy scan (weeks 18–22) — Detailed check of organs, spine, brain; gender may be revealed
- Glucose screening (weeks 24–28) — Tests for gestational diabetes (affects ~6–9% of pregnancies)
- Group B strep test (weeks 35–37) — Determines if antibiotics are needed during labor
- Weekly visits (weeks 36–40) — Monitoring position, heartbeat, cervical changes
Pregnancy Costs in the United States
Understanding the financial side of pregnancy helps families prepare:
| Expense | With Insurance | Without Insurance |
|---|---|---|
| Prenatal care (all visits) | $500 – $2,000 | $2,000 – $5,000 |
| Vaginal delivery | $2,000 – $5,000 | $10,000 – $15,000 |
| C-section delivery | $3,000 – $8,000 | $15,000 – $25,000 |
| Hospital stay (2–4 days) | Included above | $5,000 – $11,000 |
| Epidural anesthesia | $200 – $500 | $1,000 – $3,000 |
Under the Affordable Care Act, most health insurance plans must cover pregnancy and newborn care as essential health benefits.
How Accurate Is the Due Date?
The due date is an estimate, not a deadline. Full-term birth spans weeks 37 through 42. Statistically:
- Only about 5% of babies are born on the exact due date
- 80% are born within 2 weeks of the due date (38–42 weeks)
- First-time mothers tend to deliver slightly later than the EDD
- The average first pregnancy lasts about 41 weeks and 1 day
An early ultrasound (before 14 weeks) is the most accurate method for confirming the due date, often more precise than LMP-based calculation.
Nutrition During Pregnancy
The American College of Obstetricians and Gynecologists (ACOG) recommends:
- Folic acid: 600 mcg daily (critical in the first trimester to prevent neural tube defects)
- Iron: 27 mg daily (supports increased blood volume)
- Calcium: 1,000 mg daily (bone development)
- DHA: 200–300 mg daily (brain development)
- Calorie increase: About 340 extra calories/day in the 2nd trimester and 450 extra in the 3rd trimester — no additional calories needed in the 1st trimester
- Weight gain: 25–35 lbs for normal BMI, 15–25 lbs for overweight, 28–40 lbs for underweight
Frequently Asked Questions
How do I calculate my due date without knowing my LMP?
If your periods are irregular or unknown, a dating ultrasound in the first trimester is the most accurate way to estimate gestational age. The ultrasound measures the crown-rump length of the fetus to determine the estimated due date.
Can my due date change?
Yes. If an early ultrasound shows a significant discrepancy (more than 7 days) from the LMP-based date, your provider may adjust the due date. Later ultrasounds are less accurate for dating because babies grow at different rates.
What is the difference between gestational age and fetal age?
Gestational age counts from the first day of your last menstrual period (includes ~2 weeks before conception). Fetal age (embryonic age) counts from actual conception and is about 2 weeks less than gestational age.
Is it safe to exercise during pregnancy?
In most healthy pregnancies, moderate exercise is recommended. The American College of Obstetricians and Gynecologists (ACOG) suggests at least 150 minutes of moderate-intensity activity per week. Walking, swimming, and prenatal yoga are popular safe choices.
How much weight should I gain during pregnancy?
The Institute of Medicine recommends 25-35 lbs for women with normal BMI, 28-40 lbs for underweight women, 15-25 lbs for overweight women, and 11-20 lbs for obese women. Your healthcare provider will give personalized guidance based on your health.
Related Tools
- Age Calculator — Calculate exact age in years, months, and days
- Date Calculator — Find the number of days between two dates
- BMI Calculator — Check your body mass index
- Daily Calorie Needs Calculator — Determine recommended daily calorie intake
- Baby Name Generator — Browse popular baby name suggestions
Sources
- ACOG — How Your Fetus Grows During Pregnancy
- Mayo Clinic — Pregnancy Week by Week
- CDC — Reproductive Health
- March of Dimes — Prenatal Care
Related Tools
- Age Calculator — Calculate exact age in years, months, and days
- Date Calculator — Find the difference between any two dates
- Sleep Cycle Calculator — Optimize your sleep during pregnancy
- Daily Calorie Needs Calculator — Adjust calorie intake for pregnancy
- BMI Calculator — Check pre-pregnancy BMI
Sources
- Mayo Clinic: Pregnancy Week by Week
- ACOG: How Your Fetus Grows During Pregnancy
- NIH: What is Prenatal Care?