Pregnancy Week Calculator

Pregnancy is counted from the first day of your last menstrual period (LMP), not from conception. To calculate how far along you are, count the number of full weeks (and extra days) from your LMP to today. Most full-term pregnancies last 40 weeks (280 days) from LMP.

By the time most women confirm pregnancy, the exact day of conception is unknown but the date of the last period is usually known. Counting from LMP gives a consistent reference point that doctors and calculators can use reliably. This means you are technically considered 'two weeks pregnant' before conception actually occurs.

This shorthand (sometimes written 12w3d) means you have completed 12 full weeks of pregnancy and are 3 days into your 13th week. Doctors and apps use this format because pregnancy progress matters down to the day, especially in the first trimester.

First trimester: weeks 1–12. Second trimester: weeks 13–26. Third trimester: weeks 27 until delivery (typically 40 weeks). This calculator shows your current trimester automatically based on your week.

37 weeks is considered early-term. 39–40 weeks is full-term. 41 weeks is late-term. 42+ weeks is post-term. Most healthy pregnancies deliver between 37 and 42 weeks — only ~5% of babies are born exactly on the estimated due date.

Yes — but for the most accurate IVF dating, use our dedicated IVF Due Date Calculator which handles Day 3, Day 5, Day 6 transfers and FET cycles. This week calculator works well for natural pregnancies and IVF pregnancies once you have a confirmed due date.