Gestational Age Calculator

It is the number of weeks and days since the first day of the last menstrual period (LMP) — written like "24 weeks and 3 days", or 24+3. Because it starts from the LMP rather than conception, gestational age is about two weeks ahead of the actual age of the embryo. A full-term pregnancy is 37 to 42 weeks.

Pregnancy is split into three trimesters: the first through 13 weeks, the second from 14 to 27 weeks, and the third from 28 weeks until birth. Each brings different milestones and prenatal checks. The calculator shows which one today's date falls in.

The weeks and days shown here are only as accurate as the last-period date behind them, and that date assumes a 28-day cycle with ovulation on day 14. Not everyone's cycle works that way, and even a cycle that is usually consistent can vary from month to month. If ovulation actually happened earlier or later than day 14, the real gestational age can be several days to over a week different from what LMP-based counting shows — that is normal variation, not an error in the calculation.

A first-trimester dating ultrasound, which measures the embryo directly, is more accurate than LMP-based counting and is what a prenatal provider uses as the reference once it is available. If an ultrasound in your prenatal chart gives a different gestational age or due date than this calculator, the scan is the number your care team will go by — this page cannot see that measurement, only estimate from the date you enter.

The due date this calculator returns is a midpoint estimate, not a deadline: full term spans 37 to 42 weeks, and most births do not land on the exact estimated date. Use the weeks-and-days figure as a personal reference — for tracking milestones or preparing questions — rather than a precise clinical record. Prenatal care is what actually confirms gestational age and tracks the pregnancy from here; this page is not a substitute for it.