How Many Weeks Pregnant Am I?

“How many weeks pregnant am I?” is the question every pregnant person asks at every appointment, because almost everything in pregnancy is measured in weeks: scans, tests, symptoms and the due date itself. The answer comes from your last period — count the weeks and days since the first day of your last menstrual period, and that is your gestational age. The due date calculator above works it out for you and shows your trimester and your progress through the 40 weeks.

This page explains how gestational age is counted, shows a week-by-week guide to what is happening, and works through examples so you can find your own week in seconds.

How Pregnancy Weeks Are Counted

Pregnancy is counted in weeks and days from the first day of your last period, not from conception. If your last period started on March 15, 2026, then on November 1, 2026 you are 33 weeks and 0 days pregnant — 231 days have passed, and 231 divided by 7 is exactly 33 weeks. The day count matters: you are 33 weeks 0 days on November 1, 33 weeks 1 day on November 2, and so on until you reach 34 weeks 0 days on November 8. Doctors write it as “33+0” and speak of being “in your 34th week” once you pass 33 weeks 0 days, which is a common source of confusion — you are in your 34th week, but you are 33 weeks pregnant.

Worked Example: LMP March 15, 2026

Last period March 15, 2026. On November 1, 2026: 231 days have passed, which is 33 weeks and 0 days. You are in your third trimester, 83% of the way through the pregnancy, with 49 days to go until the due date of December 20, 2026. Enter the same date in the due date calculator above and it shows the same figures, with a progress bar and your trimester.

Worked Example: LMP June 1, 2026

Last period June 1, 2026. On November 1, 2026: 153 days have passed, which is 21 weeks and 6 days — 153 divided by 7 is 21 with 6 left over. You are in your second trimester, 55% of the way through, with a due date of March 8, 2027. The anatomy scan, usually done at 18 to 22 weeks, would be due right about now.

Week-by-Week Guide

The table below shows what is happening at key weeks, so you can find your week and see what to expect.

The Three Trimesters

Pregnancy is divided into three trimesters, and each feels different. The first trimester runs from week 0 to week 13 and 6 days: the baby’s organs form, morning sickness peaks, and tiredness is common. The second runs from week 14 to week 27 and 6 days: energy usually returns, the bump shows, and most people feel their best. The third runs from week 28 to birth: the baby grows fastest, sleep gets harder, and appointments become weekly near the end. For a last period of March 15, 2026, the first trimester ends June 20, the second ends September 26, and the third starts September 27.

How to Work Out Your Week Without a Calculator

If you know your due date, count backwards: subtract your due date from today in weeks. If your due date is December 20, 2026 and today is November 1, there are 7 weeks to go, so you are 40 − 7 = 33 weeks pregnant. If you know your last period, count the days since it started and divide by 7. A calendar or a period-tracking app does the counting for you, but the method is simple enough to do on paper: find the date 28 days after your last period, then keep adding 28-day blocks until you pass today, and count the leftover days.

• Count from the first day of the last period, not the last day and not the conception date.
• Count in weeks and days, not just weeks — the days matter for scan windows and tests.
• Remember you are “in” the next week. At 33 weeks 0 days you are in your 34th week, but you are 33 weeks pregnant.
• Let the scan correct you. If an early scan disagrees with your count by more than a week, your doctor will use the scan date.
• Do not panic about a day or two. Due dates and week counts are estimates; a day either way changes nothing.

What Happens at Each Stage

First Trimester (Weeks 0–13)

The embryo becomes a fetus, the heart starts beating around week 6, and all major organs form by week 12. Morning sickness affects about 70% of pregnant people, usually worst between weeks 6 and 12. The dating scan at 11 to 14 weeks sets the due date. Folic acid matters most in these weeks, because the neural tube closes by week 6 — often before you know you are pregnant.

Second Trimester (Weeks 14–27)

Energy returns, nausea usually fades, and the bump becomes visible. The anatomy scan at 18 to 22 weeks checks the baby’s organs in detail. Most people first feel movement between weeks 18 and 22. Glucose screening happens at 24 to 28 weeks. This is the most comfortable trimester for most people, and the best time for travel and for preparing the nursery.

Third Trimester (Weeks 28–40)

The baby gains weight fast — about 200 g a week in the final weeks — and the lungs mature. Sleep gets harder as the bump grows, and appointments become fortnightly, then weekly. The baby usually turns head-down by week 36. Early term starts at 37 weeks, full term at 39 weeks, and the due date is at 40 weeks. Your daily water intake matters more than ever in these weeks, and your calorie needs are about 450 a day above normal in the third trimester.

Common Confusions About Pregnancy Weeks

• “I am 4 weeks pregnant but I conceived 2 weeks ago.” Correct. The count starts at the last period, two weeks before conception.
• “My app says 33 weeks but my doctor says 32.” Different counting methods or a scan-adjusted date. Ask which date your doctor is using and use that one.
• “I do not know my last period.” Use the conception date plus 266 days, or let an early ultrasound set the date.
• “My due date changed after the scan.” Normal. If the scan disagrees by more than seven days, the scan date wins.
• “I am past my due date.” Only 5% of babies arrive on the date. Most arrive within two weeks either side, and induction is usually discussed after 41 weeks.

Related tools: your due date and milestones from the due date calculator, your daily water intake in pregnancy and your calorie needs. The American College of Obstetricians and Gynecologists explains how pregnancy is dated.

Quick Reference

Keep the reference figures below handy while you plan.

What to remember

• Your due date is 280 days after the first day of your last period, or 266 days after conception.
• Only about 5 percent of babies arrive on their due date — most arrive within two weeks either side.
• A longer cycle pushes the due date later: a 35-day cycle adds seven days.
• An ultrasound before 14 weeks is the most accurate way to date a pregnancy.
• Full term is 39 to 40 weeks; early term is 37 to 38 weeks.

Your checklist

1. Enter the first day of your last period, or your conception date, in the calculator above.
2. Note your due date, your trimester dates and your milestones.
3. Book your first prenatal appointment before 10 weeks.
4. Ask about the dating scan at 11 to 14 weeks.
5. Have the hospital bag ready by 37 weeks.

Mistakes to avoid

• Counting from the last day of the period instead of the first day.
• Forgetting the cycle-length adjustment when cycles are not 28 days.
• Treating the due date as an appointment — it is an estimate.
• Panicking when the scan changes the date — that is normal and means the dating improved.
• Planning everything for the exact due date with no slack either side.

Frequently Asked Questions

How many weeks pregnant am I?

Count the weeks and days since the first day of your last period. If your last period started March 15, 2026, then on November 1, 2026 you are 33 weeks and 0 days pregnant. The calculator above works it out from your last period or conception date.

Why am I counted as pregnant before conception?

Because pregnancy is dated from the first day of the last period, about two weeks before conception. Ovulation usually happens around day 14 of the cycle, so the 40-week count includes those two weeks. It is a convention that makes dating possible when the conception date is unknown.

What trimester am I in?

The first trimester is weeks 0 to 13 and 6 days, the second is weeks 14 to 27 and 6 days, and the third is week 28 to birth. If you are 33 weeks pregnant, you are in your third trimester.

How do I work out my due date from my weeks?

Add the weeks remaining to 40. If you are 33 weeks pregnant, you have 7 weeks to go, so your due date is 7 weeks from today. More precisely, add 280 days to the first day of your last period.

Is my week count wrong if my cycles are irregular?

It can be. The count assumes a 28-day cycle with ovulation on day 14. If your cycles are longer or irregular, the count can be off by days or even a week. An ultrasound before 14 weeks gives the most accurate dating.

What week is the anatomy scan?

Usually 18 to 22 weeks. It checks the baby’s organs, growth and position in detail. For a last period of March 15, 2026, the window is July 19 to August 16, 2026.

Disclaimer: This calculator provides estimates for general information only and is not medical advice. Pregnancy dating is approximate and an early ultrasound is the most accurate method. Talk to your doctor or midwife about your pregnancy, scans and any concerns.