How pregnancy weeks are counted
Pregnancy is dated from the first day of your last menstrual period, not from conception. This means you're already "2 weeks pregnant" on the day you actually conceive - and by the time you miss a period and get a positive test, you're usually 4 to 5 weeks along.
Pregnancy weeks are expressed as "weeks + days." If your LMP was 70 days ago, you are 10 weeks + 0 days pregnant. If 75 days ago, you are 10 weeks + 5 days. The calculator above does this math from either your LMP or your due date.
What happens each trimester
- First trimester (weeks 1–13): all major organs form. Symptoms can include nausea, fatigue, breast tenderness, and frequent urination. Miscarriage risk is highest in this window.
- Second trimester (weeks 14–27): often called the "honeymoon" trimester. Nausea usually fades, energy returns, and a bump becomes visible. The anatomy scan happens around week 20.
- Third trimester (weeks 28–40+): rapid baby growth, more frequent prenatal visits, increasing discomfort. Most babies arrive between weeks 37 and 42.
Frequently asked questions
How are pregnancy weeks counted?
Pregnancy is counted in weeks and days from the first day of your last menstrual period (LMP), not from conception. So when you're 8 weeks pregnant, the embryo is actually about 6 weeks old. This is the standard obstetric convention worldwide.
What week of pregnancy am I in?
Count the number of full weeks since the first day of your last period. For example, if it's been 75 days, you're 10 weeks + 5 days pregnant (75 ÷ 7 = 10 remainder 5). The calculator above does this automatically - just enter your LMP or due date.
How long is a full pregnancy in weeks?
A full-term pregnancy lasts 40 weeks counted from LMP - about 38 weeks from conception. Pregnancy is considered full term anywhere from 37 to 42 weeks. Babies born before 37 weeks are preterm; those born after 42 are post-term.
What are the three trimesters?
First trimester: weeks 1 through 13. Second trimester: weeks 14 through 27. Third trimester: weeks 28 through delivery. Each trimester is roughly 13 weeks. Symptoms, baby development, and prenatal care milestones differ in each.
When can I find out my baby's sex?
Non-invasive prenatal testing (NIPT) from a blood draw can determine sex as early as 9–10 weeks. An ultrasound can usually identify external genitalia around 18–20 weeks (the anatomy scan). Some clinics offer earlier private gender scans from 14–16 weeks.
When will I feel the baby move?
First-time parents usually feel movement (called quickening) between weeks 18 and 22. People who have been pregnant before often feel it earlier, around 16 weeks, because they recognize the sensation. Early movements feel like flutters, bubbles, or popcorn popping - not yet the unmistakable kicks of later pregnancy.
These calculators give estimates based on cycle averages and standard formulas. They are for general information only and are not medical advice. For anything concerning your health or pregnancy, talk to a qualified healthcare provider.