1. What is the What to Expect Due Date Calculation?

The What to Expect method calculates the estimated due date by adding 280 days (40 weeks) to the first day of the last menstrual period (LMP). This is based on the typical 40-week human gestation period.

2. How Does the Calculator Work?

The calculator uses the simple formula:

Where:

• LMP — First day of last menstrual period
• 280 days — Standard length of pregnancy (40 weeks)

Explanation: This method assumes a regular 28-day menstrual cycle with ovulation occurring on day 14.

3. Importance of Due Date Estimation

Details: An accurate due date helps healthcare providers monitor fetal development, schedule important tests, and determine if the pregnancy is progressing normally.

4. Using the Calculator

Tips: Enter the first day of your last menstrual period (LMP) in the format YYYY-MM-DD. The calculator will add 280 days to estimate your due date.

5. Frequently Asked Questions (FAQ)

Q1: How accurate is this due date calculation?
A: Only about 5% of women deliver on their exact due date. Most deliver within 2 weeks before or after.

Q2: What if my cycle isn't 28 days?
A: This calculation works best for women with regular 28-day cycles. If your cycle is longer or irregular, an ultrasound may provide a more accurate due date.

Q3: Why 280 days/40 weeks?
A: Pregnancy is traditionally calculated from LMP, which is about 2 weeks before conception actually occurs.

Q4: When will my healthcare provider adjust my due date?
A: Providers often adjust based on first-trimester ultrasound measurements, which can be more accurate than LMP dating.

Q5: What's the difference between this and Naegele's rule?
A: This is essentially the same as Naegele's rule, which adds 7 days to LMP then subtracts 3 months (equivalent to 280 days).