1. What is the NHS Due Date Calculation?

The NHS due date calculation estimates pregnancy due date by adding 280 days (40 weeks) to the first day of the last menstrual period (LMP). This follows the standard method used by the UK National Health Service.

2. How Does the Calculator Work?

The calculator uses the simple formula:

Where:

• LMP — First day of last menstrual period
• 280 days — Equivalent to 40 weeks gestation

Note: This assumes a regular 28-day cycle with ovulation on day 14. Actual delivery date may vary by ±2 weeks.

3. Importance of Due Date Calculation

Details: Accurate due date estimation is crucial for proper prenatal care scheduling, growth monitoring, and timing of important tests during pregnancy.

4. Using the Calculator

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

5. Frequently Asked Questions (FAQ)

Q1: What if my cycle isn't 28 days?
A: The calculation assumes a 28-day cycle. For irregular cycles, an early ultrasound may provide better dating.

Q2: How accurate is this calculation?
A: Only about 5% of women deliver on their exact due date. Most deliver within 2 weeks before or after.

Q3: What if I don't know my LMP?
A: Contact your healthcare provider who may recommend a dating ultrasound scan.

Q4: Does this account for leap years?
A: Yes, the calculator automatically accounts for leap years in the calculation.

Q5: Why 280 days specifically?
A: This represents the standard 40-week gestation period used in obstetrics (including 2 weeks before conception).