Due Date Calculator

Due date = Last Menstrual Period (LMP) + 280 days (40 weeks). This is Naegele's rule. If your LMP was January 1, your due date is October 8. The calculator also works from conception date (add 266 days) or ultrasound measurements.

Only about 5% of babies are born on their exact due date. 80% are born within 2 weeks before or after. The due date is an estimate based on a 28-day cycle. Irregular cycles, late ovulation, or IVF dates may shift the actual due date.

Use conception date if known (add 266 days). Or use the first ultrasound dating (most accurate in the first trimester, within ±5 days). The calculator accepts LMP, conception date, or ultrasound date as input for the most accurate estimate.

First trimester: weeks 1-12 (months 1-3). Second trimester: weeks 13-26 (months 4-6). Third trimester: weeks 27-40 (months 7-9). The calculator shows your current week, trimester, and days remaining based on your due date.

For IVF: Due date = Transfer date + (280 - embryo age in days). Day 3 transfer: add 263 days. Day 5 transfer: add 261 days. This is more accurate than LMP-based calculation because the conception date is precisely known.