Pregnancy Due Date Calculator

How to use it

• If you know the first day of your last period and your cycles are fairly regular, use the LMP method — it is what most doctors start with.
• If you conceived through timed intercourse, IUI or know your ovulation date, the conception method is more precise.
• If you have had an early ultrasound, use the scan method and enter the gestational age the radiologist wrote on the report. Below 14 weeks this is the most accurate method of all.

What it estimates — and what it cannot

• The LMP method uses Naegele’s rule: 280 days from the first day of the last period, adjusted here for cycles that are not 28 days.
• Only about 4 in 100 babies arrive exactly on the due date. A normal term birth is anywhere from 37 to 42 weeks.
• If your dating scan disagrees with your LMP by more than about a week in the first trimester, your doctor will usually re-date the pregnancy from the scan.
• Twins, IVF pregnancies and pregnancies conceived soon after stopping contraception often need dating confirmed on ultrasound rather than by dates alone.

When to see your obstetrician

Book your first antenatal visit as soon as a home test is positive — ideally before 8 weeks. Come in urgently, at any stage, if you have bleeding, severe abdominal pain, high fever, severe vomiting that stops you keeping fluids down, a bad headache with blurred vision or swelling, leaking fluid, or (after 28 weeks) reduced fetal movements.