Pregnancy Week Calculator
Enter the first day of your last menstrual period to see your current pregnancy week, approximate months, due date, trimester, and progress percentage.
Understanding Pregnancy Weeks
Pregnancy is counted from the first day of your last menstrual period (LMP), not from the date of conception. Since conception typically occurs about 2 weeks after the LMP, the gestational age is approximately 2 weeks more than the actual fetal age. Medical professionals worldwide use this LMP-based system because most women can reliably recall their last period date, while the exact ovulation or conception date is often uncertain.
Pregnancy Weeks = (Today - Last Menstrual Period) / 7
Quotient = weeks, Remainder = days (e.g., 65 days = 9 weeks 2 days)
Approximate months = weeks / 4 (providers prefer tracking by weeks)
Fetal Development Chart (by 4-week intervals)
| Week | Trimester | Size / Weight | Key Developments |
|---|---|---|---|
| 4 | 1st | 0.04 in | Implantation complete, gestational sac forms |
| 8 | 1st | 0.6 in / <0.1 oz | Heartbeat starts, arm and leg buds form |
| 12 | 1st | 2.4 in / 0.6 oz | Major organs complete, fingers and toes develop |
| 16 | 2nd | 4.7 in / 3.9 oz | Gender identifiable, first movements felt |
| 20 | 2nd | 10 in / 10.6 oz | Hearing develops, active kicking begins |
| 24 | 2nd | 12 in / 1.3 lb | Lung development begins, eyes can open |
| 28 | 3rd | 14 in / 2.2 lb | Rapid brain development, viability reached |
| 32 | 3rd | 16 in / 4 lb | Lungs maturing, rapid weight gain |
| 36 | 3rd | 18.5 in / 5.5 lb | Fat layer builds, immune antibodies transfer |
| 40 | Full Term | 20 in / 7.3 lb | Ready for delivery, head-down position |
Trimester-by-Trimester Guide
First Trimester (Weeks 1-13)
- Morning sickness (nausea/vomiting) is most severe at weeks 6-12 and usually improves after week 13.
- Extreme fatigue and sleepiness are common; prioritize rest and sleep.
- Miscarriage risk is highest during this period -- avoid alcohol, tobacco, and heavy lifting.
- Begin taking prenatal vitamins with folic acid (400-800 mcg/day) ideally before conception.
Second Trimester (Weeks 14-27)
- Nausea subsides and appetite returns -- often called the "honeymoon period" of pregnancy.
- You may start feeling baby movements (quickening) around weeks 16-22; first-time mothers may notice it later.
- Healthy weight gain is about 0.5-1 lb per week during this period.
- Schedule your anatomy scan (18-22 weeks) and gestational diabetes screening (24-28 weeks).
Third Trimester (Weeks 28-40)
- The baby gains weight rapidly; you may experience back pain, swelling, and Braxton Hicks contractions.
- Braxton Hicks (practice contractions) are normal, but contact your provider if they become regular and intense.
- Weekly prenatal visits begin at week 36, with Non-Stress Tests (NST) to monitor fetal well-being.
- Prepare your hospital bag, install the car seat, and have a birth plan finalized by week 36.
Recommended Prenatal Visit & Test Schedule (ACOG)
| Timing | Tests / Screenings | Notes |
|---|---|---|
| 6-8 weeks | First ultrasound, blood type, CBC, STI panel | Confirm pregnancy, baseline health |
| 11-13 weeks | NT scan + first trimester screen | Nuchal translucency, chromosomal screening |
| 15-20 weeks | Quad screen / NIPT (optional) | Down syndrome & neural tube defect screening |
| 18-22 weeks | Anatomy scan (detailed ultrasound) | Evaluate fetal structures and organs |
| 24-28 weeks | Glucose challenge test (GCT) | Gestational diabetes screening |
| 28-32 weeks | Growth ultrasound, Rh antibody recheck | Fetal growth assessment, amniotic fluid check |
| 35-37 weeks | GBS culture, NST | Group B strep screening, fetal monitoring |
| 37-40 weeks | Weekly NST + cervical checks | Monitoring and delivery planning |
Pregnancy Nutrition by Trimester
| Period | Key Nutrient | Daily Amount | Food Sources |
|---|---|---|---|
| Pre-conception - 12 wk | Folic Acid | 400-800 mcg | Spinach, broccoli, fortified cereals, supplements |
| 12 wk - delivery | Iron | 27 mg | Lean red meat, beans, spinach, supplements |
| 20 wk - delivery | Calcium | 1,000 mg | Milk, cheese, yogurt, fortified juices |
| All trimesters | DHA (Omega-3) | 200-300 mg | Salmon, sardines, walnuts, supplements |
| All trimesters | Vitamin D | 600 IU | Sunlight, fortified milk, eggs, supplements |
Recommended total weight gain during pregnancy depends on pre-pregnancy BMI (IOM guidelines): underweight (BMI <18.5) should gain 28-40 lbs, normal weight (BMI 18.5-24.9) should gain 25-35 lbs, overweight (BMI 25-29.9) should gain 15-25 lbs, and obese (BMI 30+) should gain 11-20 lbs. Report sudden weight gain (more than 2 lbs/week) or no weight gain over 2 weeks to your provider.