How Your Due Date is Estimated

The due date calculation is an estimation based on standard pregnancy lengths. The method varies depending on the input you provide.

• Last Menstrual Period (LMP) Method: This is the most common method. It assumes a standard 28-day menstrual cycle and ovulation on day 14. The estimated due date is calculated by adding 280 days (40 weeks) to the first day of your LMP.
• Conception Date Method: If you know the exact date of conception, the calculator adds 266 days (38 weeks) to this date. This is the average length of a pregnancy from the moment of conception.

Current progress (gestational age) is calculated from the start of the LMP (either the actual date or an approximation if using conception date) to today. Trimesters are divided as follows: 1st (0-13 weeks), 2nd (14-27 weeks), and 3rd (28+ weeks).

Example Calculation

Based on your inputs, here's how the estimation was made:

• Calculation Method: Last Menstrual Period
• Date Provided: December 1, 2025

We added 280 days (40 weeks) to your LMP date, December 1, 2025, to estimate your due date as September 7, 2026.

Counting from December 1, 2025 to today gives 0 days, which is 0 full weeks and 0 extra days. That places the pregnancy in trimester 1.