Gestational Age Calculator
Calculate gestational age in weeks and days from LMP to any date — runs in your browser.
What gestational age means
Gestational age is the number of completed weeks (and remaining days) since the first day of the last menstrual period (LMP). Even though conception happens roughly two weeks after the LMP, obstetric convention always counts from the LMP because it is the most reliably known date. A full-term pregnancy is 40 weeks gestational age.
The reference date defaults to today so you can see your current gestational age immediately. Adjust it to a future date to preview your gestational age at an upcoming scan or appointment. The trimester shown is the standard breakdown: first (weeks 0-12), second (weeks 13-26), third (week 27 onward).
FAQ
Why does pregnancy start counting from LMP rather than conception? Conception date is rarely known with certainty, while the LMP date is recorded at the first prenatal visit. Using LMP gives a consistent reference point across all pregnancies.
My dating scan showed a different gestational age — which is correct? Ultrasound measurements of the baby can be more accurate than LMP dating, especially if cycles are irregular. Your healthcare provider will advise on which date to use.
What counts as the start of the third trimester? Guidelines vary slightly; this tool uses week 27 (day 189) as the start of the third trimester.
Not medical advice. This tool provides estimates only. Always consult a qualified healthcare provider for clinical decisions.