Find out how far along you are in weeks and days, which trimester you're in, your due date, and your estimated conception date.
Progress through a 40-week pregnancy
Dating is based on a 40-week pregnancy counted from the last menstrual period (Naegele's rule) and assumes a regular 28-day cycle, so it's an estimate. Your provider's ultrasound dating is more accurate and takes priority. Conception date is approximate. This tool is for educational purposes only and is not medical advice — please confirm your dates and care with your OB-GYN or midwife.
Pregnancy is measured in gestational age, counted from the first day of your last menstrual period — not from conception. That's why you're considered about two weeks "pregnant" before conception actually happens: it gives doctors a consistent starting point, since the last period is easier to date than ovulation.
A full-term pregnancy is around 40 weeks, or 280 days, from that first day. The calculator works out how many weeks and days have passed, and projects your due date using the same standard method.
The due date here uses Naegele's rule: add 280 days to the first day of your last period. If you enter a due date instead, the calculator works backward to estimate your last period and current progress.
This assumes a regular 28-day cycle with ovulation around day 14. If your cycles are longer or shorter, the date shifts, which is one reason an early ultrasound is used to confirm or adjust dating.
Pregnancy is divided into three trimesters. The first runs through week 13, the second from weeks 14 to 27, and the third from week 28 until birth. Each brings different developmental milestones and different things your care team watches for.
Knowing your week and trimester helps you follow along with what's happening and prepare for the appointments and screenings that tend to cluster at certain stages.
An early ultrasound measures the baby directly and is generally more accurate than period-based dating, especially in the first trimester. If your cycle is irregular or you're unsure of your last period, the scan may move your due date by days or more.
When the ultrasound and last-period dates disagree, providers usually go with the ultrasound. Treat this calculator's result as a helpful estimate that your appointments will refine.
Your gestational age is the reference point for prenatal care: it guides when screenings and tests are offered, how growth is tracked, and what to expect next. It's also how pregnancy apps and books organize their week-by-week information.
For anything about your health or the pregnancy, your OB-GYN or midwife is the right source — this tool simply helps you see roughly where you are.
Count from the first day of your last period: a full term is about 40 weeks. Enter that date, or your due date, above and the calculator gives your weeks and days.
Gestational age is counted from the last period, about two weeks before ovulation, because that date is easier to pinpoint. So you're "two weeks pregnant" around the time of conception.
The 40-week estimate is a guide; few babies arrive exactly on it. An early ultrasound gives more accurate dating, particularly if your cycle is irregular.
Longer or shorter cycles shift ovulation and the dates, so the estimate may be off by a few days. An ultrasound can confirm or adjust your dating.
The first trimester is through week 13, the second is weeks 14 to 27, and the third is week 28 onward until birth.