Question 1

How is the due date calculated?

Accepted Answer

Using Naegele's Rule: Due Date = LMP + 280 days + (cycle length − 28 days). For a standard 28-day cycle, this is simply LMP + 280 days (40 weeks). If your cycle is 35 days, it becomes LMP + 287 days. This is the most widely used method worldwide and the standard formula used by obstetric care providers.

Question 2

How accurate is the estimated due date?

Accepted Answer

Only about 5% of babies are born on their exact due date. A full-term birth normally occurs anywhere between 37 and 42 weeks. The due date is a midpoint estimate, not a deadline. An ultrasound scan — especially in the first trimester — provides a more precise estimate by measuring the baby's size directly.

Question 3

What are the three trimesters?

Accepted Answer

1st Trimester: Weeks 1–12 (organ formation, highest miscarriage risk). 2nd Trimester: Weeks 13–26 (baby grows rapidly, movement felt, anatomy scan). 3rd Trimester: Weeks 27–40 (baby gains weight, lungs mature, birth preparation). Full term is defined as 37–42 weeks.

Question 4

What if my cycle is not 28 days?

Accepted Answer

Our calculator adjusts automatically. Each day your cycle differs from 28 adds or subtracts one day from the due date. Example: 35-day cycle → due date is 7 days later than the standard calculation. Use the slider to set your actual average cycle length between 20 and 45 days.

Question 5

Should I consult a doctor even if this calculator shows a result?

Accepted Answer

Yes, always. This calculator provides an estimate for informational purposes only. Your doctor or midwife will confirm your due date using clinical examination and ultrasound, and will provide personalised prenatal care. No online tool replaces professional medical advice.

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