How Far Along Am I?

How pregnancy weeks are counted

The count starts on the first day of your last menstrual period, not on the day you conceived. That is deliberate: the first day of a period is a date almost everyone can recall, while ovulation and conception happen about two weeks later and are rarely known exactly. Because of that convention, the first two weeks of "pregnancy" pass before conception occurs, and a pregnancy dated at 4 weeks is only about 2 weeks post-conception.

Your gestational age is written as weeks plus days, 26w3d means 26 completed weeks and 3 days. A pregnancy reaches 40 weeks (280 days) at the estimated due date, and that estimate assumes a 28-day cycle with ovulation on day 14. If your cycle is longer or shorter, the estimate shifts by roughly the same number of days, which is why a dating ultrasound often replaces the calendar calculation.

The calculator above works in both directions. If you know the first day of your last period, it counts forward to today and gives you the weeks and days. If you already have a due date from your provider or an ultrasound, it works backward to show your current gestational age and what your last period date would have been. Dates are handled as plain calendar days, so nothing is thrown off by time zones. The CDC's pregnancy health pages cover the same timeline in more detail.

This page is a reference estimate, not medical advice. Your provider's dating is the one that counts for tests, scheduling and any decision that matters.

Worked example: last period started March 3, 2026

Put March 3, 2026 into the calculator as the first day of the last period, with a 28-day cycle. Assuming today is October 16, 2026, the math runs like this:

• Days since the last period started: 227 days
• Gestational age: 227 ÷ 7 = 32 completed weeks, remainder 3 days, so 32w3d
• Trimester: third, because the third trimester begins at 28w0d
• Estimated due date: March 3, 2026 + 280 days = December 8, 2026
• Days remaining to the due date: 53 days, which is 7 weeks and 4 days

Two details are worth pulling out of that. First, 32w3d is not "32 weeks" and it is not "33 weeks", rounding in either direction moves you a week, and week-by-week guidance is written against the exact number. Second, the 53 days remaining is more useful than the due date itself for planning: it tells you that you are inside the last two months and past the point at which most providers want you thinking about a hospital bag.

Now push the cycle length to 32 days instead of 28. The due date moves four days later, to December 12, 2026, and today's gestational age drops to 32w3d minus 4 days, or 31w6d. A four-day change in cycle length moves you four days in the count, small, but enough to change which week's guidance applies to you.

Worked example: due date of November 20, 2026

If you already have a due date, the calculator runs the arithmetic backward. With a due date of November 20, 2026 and a 28-day cycle:

• First day of the last period: November 20, 2026 minus 280 days = February 13, 2026
• Gestational age on October 16, 2026: 35w0d
• Trimester: third
• Days until the due date: 35 days, or exactly 5 weeks
• Estimated conception date: around February 27, 2026, about two weeks after the last period

At 35w0d you are in the window where a baby born now would be described as late preterm rather than premature, and most providers would not try to stop labor. The full-term window for this pregnancy runs from 37w0d, which is October 30, 2026, through 42w0d, which is December 4, 2026. A baby arriving anywhere in that window is at term or later, and the due date sits comfortably in the middle of it.

This backward calculation is also the quickest way to sanity-check a due date you were given. If subtracting 280 days lands on a date that does not match your memory of your last period, one of the two numbers is wrong, usually a cycle-length assumption rather than a typo. Ask your provider which dating method they used before you plan anything around the date.

Trimesters, weeks and what counts as full term

Trimesters are bookkeeping, but they matter because guidance, screening schedules and leave paperwork are all written against them. Here is the standard breakdown.

Notice that "full term" is not 37 to 42 weeks. The American College of Obstetricians and Gynecologists narrowed the definition years ago because babies born at 37 and 38 weeks do measurably less well than those born at 39 and 40. ACOG's patient guidance on calculating a due date sets out the definitions in full.

Why your due date moves, and what that means for your weeks

Due dates get revised more often than people expect, and every revision moves your week count with it. The most common cause is a dating ultrasound. If a first-trimester scan measures the baby more than about 7 days away from the calendar estimate, most providers adopt the ultrasound date instead. In the second trimester the threshold widens, often to 10 or 14 days, because later measurements are less precise.

Cycle length is the second cause. The 280-day rule assumes ovulation on day 14 of a 28-day cycle. Ovulation on day 21 of a 35-day cycle means conception happened a week later than assumed, so the calendar estimate is a week early and gets corrected. Irregular cycles make the calendar estimate unreliable in the first place, which is why an early scan is usually recommended.

Twins and higher-order multiples are a third case. The dating method is the same, but the expected delivery date is not: twins are commonly delivered around 36 to 37 weeks, and triplets earlier. That means a 35-week twin pregnancy is close to term, while a 35-week singleton is still late preterm. The number of weeks means something different depending on how many babies you are carrying.

Once your provider settles on a date, use that date everywhere, in this calculator, in any app, and in anything you write down. Mixing a calendar estimate with a scan-adjusted date produces exactly the few-days discrepancies that make people think an app is wrong when it is not. For the broader picture on prenatal care timing, the March of Dimes prenatal care guide is a good plain-English reference.

What the week count is used for

Knowing you are 32w3d is not trivia, it drives a series of decisions. Screening and testing: first-trimester combined screening happens between roughly 11 and 14 weeks, the anatomy scan between 18 and 22, and group B strep screening around 36 to 37. Each of those has a window, and the window is set in weeks and days. Medication and travel: many airlines restrict flying after 36 weeks for singletons and earlier for twins, and some medications are avoided in specific trimesters.

Leave and paperwork: short-term disability, FMLA and employer leave policies are written around weeks of pregnancy or weeks of recovery, and a claim filed at the wrong week gets kicked back. Monitoring: from about 28 weeks onward, providers start counting fetal movements, and from 41 weeks many will offer extra monitoring or induction.

The practical takeaway is to keep the exact number, not the rounded one. "About eight months" is fine for a family conversation; 32w3d is what goes on a form. If you want to convert your weeks into the months people ask about, the rough mapping is weeks 18 to 22 for 4 to 5 months, 23 to 27 for 6 months, 28 to 31 for 7 months, 32 to 35 for 8 months, and 36 to 40 for 9 months, but keep the weeks as the real number.

This calculator is a general reference estimate and not medical advice, and it cannot account for your individual pregnancy. Always follow the dating and schedule your own provider gives you.