Gestational Age Calculator
Calculate gestational age from the first day of your last menstrual period (LMP). Track your pregnancy week by week and see your trimester progress.
First Trimester
What is Gestational Age?
Gestational age is the measure of how far along a pregnancy is, typically calculated from the first day of the last menstrual period (LMP) to the current date. A full-term pregnancy is approximately 40 weeks (280 days).
Pregnancy is divided into three trimesters: the first trimester (weeks 1-12), second trimester (weeks 13-28), and third trimester (weeks 29-40). Each trimester brings different developmental milestones for the baby and different experiences for the mother.
Our gestational age calculator uses your LMP date to calculate the current gestational age in weeks and days, shows your progress bar toward 40 weeks, and tells you which trimester you're in. Ultrasound measurements can also be used to confirm gestational age, especially in early pregnancy.
Frequently Asked Questions
How is gestational age calculated from LMP?
Gestational age is calculated by counting the number of days between the first day of your last menstrual period (LMP) and today. This method, known as Naegele's rule, assumes a 28-day cycle with ovulation on day 14. Your estimated due date is LMP plus 280 days (40 weeks).
What is the difference between gestational age and fetal age?
Gestational age counts from the first day of your LMP (about 2 weeks before conception), while fetal age counts from the actual conception date. Fetal age is therefore about 2 weeks less than gestational age. Healthcare providers always use gestational age for consistency and standardization.
What trimester am I in based on my weeks of pregnancy?
First trimester: weeks 0 to 13 (fetal organs develop, highest risk of miscarriage). Second trimester: weeks 14 to 27 (baby grows, you may feel movement). Third trimester: week 28 to birth (baby gains weight, organs mature). Our calculator shows your current trimester automatically.
How accurate is LMP-based due date calculation?
LMP-based dating is reasonably accurate for women with regular 28-day cycles but can be less reliable for irregular cycles or unknown LMP dates. Early ultrasound dating (first trimester) is considered more accurate and may adjust the due date if the difference is more than 5-7 days.
Is my due date information stored?
No. All calculations happen entirely in your browser. Your LMP date is never sent to any server, stored, or shared. This calculator is 100% private and processes everything client-side.