🤱 Due Date Calculator

Calculate your pregnancy due date from last menstrual period.

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What is Due Date Calculator?

Expecting parents often want a quick estimate of when their baby is likely to arrive, and this calculator gives you exactly that using the same method doctors have relied on for over a century. Rather than needing an ultrasound on day one, you can get a preliminary due date from a single piece of information you already know — the first day of your last menstrual period.

Naegele's Rule Formula

The calculator adds 280 days (40 weeks) to the first day of your last menstrual period (LMP), which assumes a fairly standard 28-day cycle with ovulation around day 14:

Estimated Due Date = LMP + 280 days

Worked Example

If your last menstrual period began on 1 January 2026:

Due Date = 1 January 2026 + 280 days = 8 October 2026

That gives an estimated delivery window centred around early October, roughly nine calendar months and one week after the LMP date.

How to Use This Calculator

  1. Select the first day of your last menstrual period using the date field.
  2. Click Calculate.
  3. View your estimated due date instantly.

Things to Keep in Mind

Naegele's rule is a useful starting estimate, but it assumes a textbook-perfect 28-day cycle — actual delivery dates commonly fall anywhere from about two weeks before to two weeks after this calculated date, and fewer than 5% of babies arrive on the exact predicted day. Irregular cycles, PCOS, or uncertainty about your LMP date can shift the accuracy of this estimate further. Always confirm your due date with a gynaecologist through an early ultrasound, which dates the pregnancy using foetal measurements rather than menstrual history alone.

💡 Tip: If your cycles are longer or shorter than 28 days, mention that to your doctor — they'll usually adjust the estimated date accordingly during your first prenatal visit.

Trying to plan around ovulation instead? The Ovulation Calculator covers that from the same LMP starting point.

📅 Last reviewed: July 2026 · Formulas verified against RBI/SEBI/IT Dept guidelines.