Pregnancy Due Date Calculator — Week by Week

Estimating your due date

The tool applies Naegele's rule (LMP + 280 days), the convention described by the American College of Obstetricians and Gynecologists (ACOG Committee Opinion No. 700, 2017). ACOG also states that first-trimester ultrasound is the most accurate method and should confirm or correct that date. If your usual cycle differs from 28 days, the calculator shifts every date by the difference. Franz Karl Naegele published the rule in 1812.

Key fields

• LMP Enter the first day of your last menstrual period.
• Cycle length The rule assumes 28 days. If your cycles are regular but different, adjust to refine the estimate.
• Current week the calculator shows how many weeks and days pregnant you are today and the dates of each trimester (first up to 13+6, second 14+0 to 27+6, third from 28+0).

Interpretation

The estimated due date is indicative. Many pregnancies conclude between weeks 38 and 41. Use the timeline to plan key milestones (scans, tests, birth plan).

Recommendations

• Share the estimate with your care team and confirm gestational age with ultrasound.
• Update the reference date after each check-up to track pregnancy progress.