Expecting a new baby is an exciting journey filled with developmental milestones. During prenatal checkups, healthcare providers refer to your pregnancy stage in terms of gestational weeks and days. Since the exact day of ovulation or conception can be difficult to pinpoint, standard clinical tracking counts the weeks from your last menstrual period. This tool helps map your gestational timeline.
By medical convention, a standard pregnancy lasts approximately 40 weeks (280 days). Gestational age is calculated starting from the first day of your last menstrual period (LMP).
Because conception typically occurs about two weeks after your period starts, you are not technically pregnant during the first two weeks of gestational age. However, this starting point is used because the first day of a period is a clear, memorable date, whereas the day of ovulation is often unknown.
To track recommended maternal weight targets throughout these weeks, try our pregnancy weight gain tracker. To estimate the date of conception, visit our pregnancy conception calculator.
The 40-week gestation timeline is divided into three structural stages called trimesters, each characterized by specific milestones: - First Trimester (Weeks 1 to 12): The fertilized egg divides rapidly, organs begin to form, and the heart starts beating. - Second Trimester (Weeks 13 to 26): Often called the most comfortable stage. The baby grows rapidly, and the mother can begin to feel movement. - Third Trimester (Weeks 27 to 40+): The baby's lungs and brain develop fully as they accumulate fat to prepare for birth.
To calculate your estimated due date directly, try our due date estimator. To count the total number of calendar days between major milestones, visit our date intervals counter.
In 1812, German obstetrician Franz Naegele established a rule for estimating due dates.
His rule assumes an average human gestation of 280 days and a regular 28-day menstrual cycle. To estimate a due date: take the first day of the last menstrual period, add one year, subtract three months, and add seven days. If a mother has a longer or shorter cycle, the timeline shifts accordingly.
It is also important to understand that an estimated due date is only a projection. In fact, only about 4% of babies are born on their exact due date. Most natural deliveries occur within a two-week window before or after the estimated date, making the due date a useful reference point rather than a strict deadline.
To check exact clock intervals between dates, visit our exact calendar duration calculator. For simple mathematical division or product checks, try our everyday basic math helper.
Suppose the first day of your last period was February 1, 2026, and today's date is April 12, 2026.
First, calculate the total number of elapsed days: - February 1 to April 12 is 70 days.
Next, convert the days into weeks: - 70 days / 7 = exactly 10 weeks pregnant.
Calculate the estimated due date (adding 280 days to Feb 1): - Due date = November 8, 2026. The baby is currently in the first trimester, with about 25% of the gestational timeline completed.