Pregnancy Calculator
Find out how many weeks pregnant you are and which trimester you're in, based on your last period.
Pregnancy Calculator
Calculate your pregnancy progress instantly.
What This Pregnancy Calculator Does
This tool applies the standard obstetric method of counting pregnancy from the first day of the last menstrual period rather than the actual estimated conception date, since conception timing is often uncertain while the last period date is typically known with much greater confidence, making it the standard clinical reference point.
How to Use the Pregnancy Calculator
Enter the first day of your last menstrual period. Your current gestational week, current trimester, and estimated due date appear instantly once calculated, based on the standard 280-day pregnancy length counted from that reference date.
Why Pregnancy Is Counted From Last Menstrual Period Rather Than Conception
Actual conception typically occurs roughly two weeks after the last menstrual period begins, but since the exact conception date is rarely known with certainty, the medical community standardized on counting pregnancy duration from the last menstrual period instead, which is why a pregnancy is considered roughly 40 weeks even though actual fetal development spans closer to 38 weeks from conception.
Pro Tip: This calculation provides a standard estimated due date based on average pregnancy length, though actual delivery can naturally occur anywhere within a normal range around that estimated date.
Understanding the Three Trimesters
The first trimester spans weeks 1 through 12, encompassing the earliest and most sensitive period of fetal development. The second trimester spans weeks 13 through 26, often associated with reduced early pregnancy symptoms and the first noticeable fetal movements. The third trimester spans weeks 27 through birth, involving continued growth and preparation for delivery.
Why This Calculator Provides an Estimate, Not a Guaranteed Date
This calculation provides a standard estimated due date based on average pregnancy length, though actual delivery can naturally occur anywhere within a normal range around that estimated date. Regular prenatal care with a qualified healthcare provider, including ultrasound dating, generally provides a more personalized and accurate due date estimate as pregnancy progresses.
Frequently Asked Questions
This calculator counts weeks from the first day of your last menstrual period, following the standard clinical method used by obstetricians for dating pregnancy progress.
The exact conception date is rarely known with certainty, while the last menstrual period date is typically known with much greater confidence, making it the standardized clinical reference point.
A standard pregnancy is considered approximately 40 weeks, or 280 days, counted from the first day of the last menstrual period, though normal delivery timing varies somewhat around this estimate.
No, it provides a standard estimate based on average pregnancy length, and actual delivery can naturally occur within a normal range around this date, with ultrasound dating during prenatal care refining the estimate further.