Pregnancy Due Date Calculator
Enter the first day of your last period — get your estimated due date, current week of pregnancy and trimester. Everything stays on your device.
Estimate your due date
How the estimate works
The standard method — Naegele's rule — adds 280 days (40 weeks) to the first day of your last menstrual period. If your cycle isn't 28 days, the estimate shifts by the difference: a 32-day cycle moves it 4 days later, a 26-day cycle 2 days earlier. Pregnancy weeks are counted from the LMP too, which is why "week 6" begins only about four weeks after conception.
Remember it's an estimate: only about 1 in 20 babies arrives on the exact due date, and anywhere from 37 to 42 weeks is considered normal timing. A first-trimester ultrasound gives the most accurate dating — if it differs from the LMP estimate, clinicians normally trust the ultrasound.
Frequently asked questions
How is a due date calculated?
LMP + 280 days, adjusted for cycle length. Most babies arrive within two weeks either side.
What if my cycle is longer or shorter than 28 days?
Shift the due date one day for each day of difference — a 32-day cycle adds 4 days.
Is an ultrasound due date more accurate?
Yes — a first-trimester ultrasound is the most accurate dating method and usually overrides the LMP estimate.