What is Naegele's rule?

Naegele's rule estimates the due date by adding 280 days (40 weeks) to the first day of the last menstrual period. It assumes a 28-day cycle and ovulation on day 14.

Which method is most accurate?

IVF transfer dates are the most precise since the exact fertilization date is known. Ultrasound dating in the first trimester is also very accurate. LMP-based estimates can vary if your cycle is irregular.

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Due Date Calculator

Calculate your estimated due date from your last period, conception date, IVF transfer, or ultrasound. See trimester milestones and pregnancy countdown.

Last updated: April 1, 2026

Last Menstrual Period

Cycle Length

days

How to Use This Calculator

Select your calculation method: Last Menstrual Period, Conception Date, IVF Transfer, or Ultrasound.
Enter the relevant date for your chosen method.
For IVF, select whether a Day 3 or Day 5 embryo was transferred.
Click Calculate to see your estimated due date, current week, and trimester timeline.

The Formula

LMP method: Due Date = LMP + 280 days (Naegele's rule). Conception: Due Date = Conception + 266 days. IVF Day 5: Due Date = Transfer + 261 days. IVF Day 3: Due Date = Transfer + 263 days.

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Frequently Asked Questions

Only about 5% of babies are born on their exact due date. Most are born within 2 weeks before or after. The LMP method assumes a 28-day cycle with ovulation on day 14, which varies between individuals.