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Pregnancy Due Date Calculator

Estimate your due date and current gestational age from the first day of your last menstrual period (or your conception date). Results use Naegele's rule, the standard method clinicians use for an initial estimate.

Your dates

Estimated due date
Dec 1, 2026

  • How far along
  • Trimester
  • Est. conception
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How it works

The classic estimate is Naegele's rule: a pregnancy lasts about 280 days (40 weeks) from the first day of the last menstrual period (LMP):

Due date = LMP + 280 days

If your cycle isn't 28 days, the estimate is shifted by the difference. From a known conception date, the due date is about 266 days later. Gestational age is measured in weeks and days from the LMP.

Worked example

If your last period began Jan 1 with a 28-day cycle:

Frequently asked questions

How accurate is a due date?
It's an estimate, not a deadline. Only about 1 in 20 babies arrive exactly on the due date; most are born within two weeks either side. An early ultrasound gives the most accurate dating, especially if your cycles are irregular.
Why is pregnancy counted from my last period?
Because the LMP is a date most people can identify, while the exact moment of conception usually isn't known. Counting from the LMP means the first two weeks of the 40 are technically before conception — that's normal and built into the method.
Does cycle length change the due date?
Yes, slightly. Naegele's rule assumes a 28-day cycle with ovulation around day 14. If your cycles are longer or shorter, ovulation shifts, so this calculator adjusts the estimate by the difference from 28 days.

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