Due Date Calculator

The most common method: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). This is Naegele rule. Another way: add 9 months and 7 days to the LMP. The standard assumes a 28-day cycle. If your cycle is longer or shorter, adjust by the difference.

Only about 5% of babies are born on their exact due date. About 80% of births occur within 2 weeks before or after the due date. Ultrasound dating (especially in the first trimester) is considered more accurate than LMP-based calculation because it directly measures fetal size.

First trimester: Weeks 1-12 (conception to 3 months). Second trimester: Weeks 13-26 (most comfortable period for many). Third trimester: Weeks 27-40+ (baby gains weight rapidly). Full term is considered 39-40 weeks. Early term: 37-38 weeks. Late/post-term: after 42 weeks.

Week 8-10: heartbeat detectable by Doppler. Week 12: risk of miscarriage drops significantly, end of 1st trimester. Week 18-20: anatomy ultrasound, may learn sex. Week 24: viability milestone. Week 28: 3rd trimester begins. Week 36: weekly visits begin. Week 37-42: full term range.

IVF conceptions have precise dating. Women with irregular cycles may have different ovulation timing than the LMP assumes. First-trimester ultrasound can adjust the due date. Multiple pregnancies (twins/triplets) typically deliver earlier. Prior pregnancy complications, maternal health, and fetal growth also affect actual delivery timing.