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Pregnancy Due Date Calculator

Estimate your due date from your last period or conception date.

Estimated due date

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Current gestation

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What this calculator does

This tool estimates your pregnancy due date using either the first day of your last menstrual period (LMP) or an estimated conception date. It also shows how many weeks pregnant you are today, based on a standard 40-week (280-day) pregnancy.

Worked example

If your last period started on January 1, 2026 and you have a typical 28-day cycle, adding 280 days gives an estimated due date of October 8, 2026.

Common mistakes

  • Using the conception date with the LMP formula. LMP-based due dates already account for the roughly two-week gap before ovulation — don't add another 280 days to a known conception date.
  • Ignoring irregular cycles. The standard formula assumes ovulation on day 14 of a 28-day cycle; longer or shorter cycles shift the actual conception date and true due date.
  • Treating the due date as exact. Only a small fraction of babies arrive precisely on their calculated due date — most arrive within a two-week window either side.

Frequently asked questions

How accurate is a due date calculated from the last menstrual period?+

Naegele's rule (last menstrual period plus 280 days, or 40 weeks) is a widely used estimate, but only about 5% of babies are born on their exact due date. It gives a useful planning target, not a guarantee — an ultrasound dating scan is more precise if cycles are irregular.

What if my cycle isn't 28 days?+

This calculator assumes a standard 28-day cycle with ovulation around day 14. If your cycles are longer or shorter, your actual conception date — and therefore due date — may shift; using the conception-date method instead can be more accurate.

How is gestational age different from fetal age?+

Gestational age is counted from the first day of your last menstrual period, about two weeks before conception actually occurs. Fetal (conceptional) age counts from the estimated conception date instead, so it runs about 2 weeks behind gestational age.

Is this calculator a substitute for medical advice?+

No. This tool gives a general estimate for planning purposes only. Always follow the due date and dating confirmed by your doctor or midwife, which typically comes from an early ultrasound.

How many weeks pregnant am I today?+

Count the days from the first day of your last menstrual period to today, then divide by 7 — this pregnancy due date calculator does that automatically and shows the result as weeks and days alongside your estimated due date.

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