Crunch Pregnancy Due Date Calculator
Three ways to estimate a due date — from the last period, the conception date, or an ultrasound measurement — plus your current week, days remaining and the trimester milestones along the way.
How it works
A full-term pregnancy is counted as 280 days (40 weeks) from the first day of the last menstrual period — Naegele's rule — even though conception typically happens about 14 days later, which is why the conception method uses 266 days. The ultrasound method works backwards from the gestational age measured at the scan: due date = scan date + (280 − age in days). Gestational age "today" is simply the number of days since the (real or implied) LMP, split into weeks and days.
Frequently asked questions
How accurate is a due date from my last period?
Naegele's rule assumes a regular 28-day cycle with ovulation on day 14. If your cycles are longer, shorter or irregular, the estimate can be off by a week or more — which is why clinics confirm dating with an early ultrasound.
Why do the three methods give different dates?
They measure from different starting points: the last period (day 0 of the count), conception (about day 14), or a size measurement at a scan. Small differences of a few days are normal and not a cause for concern.
What week of pregnancy am I in?
Count the days since the first day of your last period and divide by 7. For example, 63 days is exactly 9 weeks. The LMP mode above shows your current week and day automatically.
When does each trimester end?
The first trimester ends at 13 weeks 6 days, the second at 27 weeks 6 days, and the third runs from 28 weeks until delivery. The table above gives the calendar dates for your pregnancy.
🌸 Planning ahead?
The Ovulation Calculator maps your fertile window and the next three cycles.