Pregnancy Calculator

1. Enter the first day of your last menstrual period (LMP) and your average cycle length.
2. If you've had an ultrasound, use the “By ultrasound” tab and enter the exam date and the weeks measured.
3. See your estimated due date, how far along you are today, and your trimester.
4. Check the dates of key prenatal milestones and tests.

The Naegele’s rule estimates your due date by adding 1 year, subtracting 3 months, and adding 7 days to the first day of your last menstrual period (LMP)—about 280 days, or 40 weeks. It assumes a 28-day cycle; for longer or shorter cycles, the calculator adjusts the date by 1 day for each day of difference. Gestational age is counted in weeks and days from your LMP.

The trimesters follow the divisions used in prenatal care: the 1st lasts through 13 weeks and 6 days, the 2nd runs from 14 weeks through 27 weeks and 6 days, and the 3rd starts at 28 weeks. A pregnancy is considered full term from 37 weeks through 41 weeks and 6 days. A first-trimester ultrasound is the most accurate way to date a pregnancy, so you can also calculate from an ultrasound.

Sources: Pregnancy handbook and primary care guidelines from the Ministry of Health, and ACOG definitions of term, consulted in 2026. This calculator is for informational purposes only and doesn’t replace a medical consultation, tests, or care from a healthcare professional.