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HWP Diagnostic

Free health tool

Pregnancy Due Date Calculator

Your due date is estimated by counting 280 days (40 weeks) from the first day of your last menstrual period - a method called Naegele's rule. Only about 1 in 20 babies arrive exactly on the due date, so treat it as a guide.

Estimate your due date and current week of pregnancy.

Uses Naegele's rule (last period + 280 days). An early ultrasound gives the most accurate dating.

Choose the first day of your last period (within the last 10 months).

This tool is for general information only and is not a diagnosis. Please consult your doctor about your results.

How accurate is the due date?

The calculation assumes a regular cycle with ovulation around day 14. If your cycles are longer or irregular, or you are unsure of your last period date, an early dating ultrasound (ideally before 14 weeks) gives a more accurate date.

Trimesters

First trimester: weeks 1-13. Second trimester: weeks 14-27. Third trimester: week 28 until birth.

Tests commonly advised in pregnancy

Your doctor will usually advise a confirmatory beta-hCG test, a complete blood count, blood group, thyroid (TSH), blood sugar and infection screening early in pregnancy, with further tests and scans in later trimesters. Always follow your obstetrician's plan.

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Frequently asked questions

How is the due date calculated?

By adding 280 days to the first day of your last period, adjusted for your cycle length if it is longer or shorter than 28 days.

Can my due date change?

Yes. Your doctor may update it after an early ultrasound, which measures the baby directly and is more accurate than the period-based estimate.

When should I take a pregnancy blood test?

A beta-hCG blood test can usually detect pregnancy about 10-12 days after conception - often before a missed period - and is more sensitive than a home urine test.