Pregnancy Calculator

About the Pregnancy Calculator

This pregnancy calculator uses Naegele's Rule to estimate your due date — the most widely accepted method used by healthcare providers worldwide. Naegele's Rule adds 280 days (40 weeks) to the first day of your last menstrual period (LMP), assuming a regular 28-day cycle with ovulation occurring on day 14. If you want to know more about your fertile window and when conception may have occurred, try our Conception Calculator or the Ovulation Calculator.

Gestational age is counted from the first day of your LMP, not from conception. This means that even before conception occurred, you are technically considered "2 weeks pregnant" by medical standards. The three trimesters divide pregnancy into: the 1st trimester (weeks 1–12), during which major organ systems develop; the 2nd trimester (weeks 13–26), often called the "honeymoon phase" of pregnancy; and the 3rd trimester (weeks 27–40), during which the baby grows rapidly in preparation for birth. If you are planning for healthy weight management during pregnancy, visit our Pregnancy Weight Gain Calculator.

The milestone dates shown above — including the anatomy scan at 20 weeks and glucose screening at 28 weeks — are standard recommendations, but your healthcare provider may schedule these tests at slightly different times based on your individual circumstances. Keep in mind that only about 5% of babies are born on their exact due date; most arrive within two weeks before or after. For accurate pregnancy dating and monitoring, always rely on ultrasound measurements and guidance from your obstetrician or midwife.