Pregnancy Week Calculator

How Many Weeks Pregnant Are You?

Pregnancy is measured in weeks and days from the first day of your last menstrual period (LMP), not from the day of conception. This means you are technically counted as two weeks pregnant at the time of conception. A full-term pregnancy lasts 40 weeks, which equals 280 days or roughly 9 months and 1 week. Enter the first day of your last period in the calculator above to see exactly how many weeks and days pregnant you are, which trimester you are in, and key upcoming milestones.

Understanding Gestational Age vs Fetal Age

Gestational age counts from your LMP and is the standard used by healthcare providers for scheduling prenatal care, tests, and delivery planning. Fetal age counts from the estimated date of conception, making it approximately two weeks shorter than gestational age. When your doctor says you are 12 weeks pregnant, they mean 12 weeks gestational age: the embryo has actually been developing for about 10 weeks. All pregnancy milestones, test schedules, and delivery considerations reference gestational age.

First Trimester: Weeks 1 Through 12

The first trimester is the period of most rapid development. By week 6, the heart begins beating. By week 8, all major organs have started forming and the embryo is officially called a fetus. By week 12, the fetus is about 2.5 inches long and has recognizable human features. This trimester brings the highest risk of miscarriage: approximately 80% of pregnancy losses occur before 12 weeks. Common symptoms include nausea, fatigue, breast tenderness, and frequent urination. The first prenatal visit typically occurs between weeks 8 and 10.

Second Trimester: Weeks 13 Through 27

Often called the most comfortable trimester, the second brings relief from first-trimester nausea and fatigue for most women. The anatomy scan ultrasound at weeks 18 to 22 checks fetal development and can reveal the baby's sex. Most women begin feeling fetal movement (quickening) between weeks 16 and 25: first-time mothers typically notice it later than experienced mothers. The fetus grows from about 3 inches to 14 inches during this trimester and develops fingerprints, eyebrows, and the ability to hear external sounds.

Third Trimester: Weeks 28 Through 40

The final trimester focuses on fetal weight gain and lung maturation. The fetus roughly doubles or triples in weight, growing from about 2.5 pounds at week 28 to 6 to 9 pounds at term. Braxton Hicks contractions (practice contractions) become common. The fetus typically moves into a head-down position by weeks 32 to 36 in preparation for delivery. Week 37 marks early term, week 39 is full term, and week 41 is late term. Most providers recommend delivery by 41 to 42 weeks due to increased risks associated with post-term pregnancy.

Key Milestones Week by Week

Week 8: first prenatal visit and potential ultrasound. Week 10 to 13: optional NIPT or first-trimester screening for chromosomal conditions. Week 16: AFP blood test offered. Week 18 to 22: anatomy scan ultrasound. Week 24 to 28: glucose tolerance test for gestational diabetes screening. Week 28: Rh-negative mothers receive RhoGAM. Week 36: Group B Strep screening. Week 37: considered early term. Week 39: full term, elective deliveries may be scheduled. Knowing where you are in this timeline helps you prepare for upcoming appointments and tests.

Prenatal Nutrition by Trimester

Nutritional needs evolve as pregnancy progresses. The first trimester requires an additional 0 calories above pre-pregnancy intake: the focus is on nutrient quality, particularly folate (600 mcg daily) to prevent neural tube defects. The second trimester adds roughly 340 extra calories per day, with increased iron needs (27 mg daily) to support expanded blood volume. The third trimester requires approximately 450 additional calories daily and increased calcium (1,000 mg) and omega-3 fatty acids for fetal bone and brain development. Prenatal vitamins fill nutritional gaps but should complement, not replace, a balanced diet rich in whole grains, lean protein, fruits, vegetables, and healthy fats.

Frequently asked questions