Find your estimated due date and trimester schedule by entering the first day of your last period.
Three Ways to Estimate a Due Date
A pregnancy due date can be estimated from the first day of the last menstrual period (LMP), from a known conception date, or from ultrasound measurements taken in the first trimester. This calculator uses the LMP method, which is the standard starting point before any scan has been done.
Why Naegele's Rule Is the Default Method
Naegele's rule adds 280 days to the LMP, based on a 28-day cycle with ovulation on day 14. Entering your own average cycle length shifts the estimate to match — a 32-day cycle pushes ovulation, conception, and the due date roughly 4 days later than the 28-day default.
When to Trust an Ultrasound Date Instead
A dating ultrasound performed between 8 and 13 weeks is generally considered more accurate than an LMP-based estimate, particularly for irregular cycles or when the LMP date is uncertain. If your doctor's ultrasound due date differs from this calculator's result by more than about a week, the ultrasound date is the one to follow.
Is the due date from LMP the same as from an ultrasound?
Not always. A dating ultrasound performed between 8 and 13 weeks is generally considered more accurate than an LMP-based estimate, particularly for irregular cycles or an uncertain LMP date.
Can I calculate my due date from the conception date instead?
Yes — if you know the conception date, the due date is roughly 266 days later. This calculator uses the LMP method, which is the standard starting point before a scan has been done.