Tools Health & Lifestyle Pregnancy Calculator
Health & Lifestyle

Pregnancy Due Date Calculator

Estimate your due date, current pregnancy week and trimester from your last menstrual period — adjusted for your cycle length.

Understanding your dates

  • A full-term pregnancy is counted as 40 weeks (280 days) from the first day of your last menstrual period — not from conception.
  • Only about 1 in 20 babies arrive exactly on the estimated due date. A normal full-term birth happens any time between 37 and 42 weeks.
  • If your cycle is longer or shorter than 28 days, the estimate shifts accordingly — this calculator adjusts for that automatically.
  • An early dating ultrasound is the most accurate way to confirm your due date; treat this estimate as a starting point.

How the due date is calculated

This calculator uses Naegele's rule, the standard method used by clinicians: it adds 280 days (40 weeks) to the first day of your last menstrual period (LMP). Because the rule assumes a textbook 28-day cycle with ovulation on day 14, the calculator also adjusts for your actual cycle length — if your cycle is 32 days, the due date moves about four days later; if it's 26 days, about two days earlier.

From the LMP it also works out how far along you are today (gestational age in weeks and days), your current trimester, your estimated conception date, and roughly how many weeks remain. Everything runs in your browser — no dates are sent anywhere.

Frequently asked questions

Why is pregnancy measured from my last period?
The exact day of conception is rarely known, but the first day of your last menstrual period is easy to identify. Clinicians standardised on LMP so that everyone measures pregnancy the same way. It means you're counted as "2 weeks pregnant" around the time of conception — which is normal and expected.
How accurate is the estimated due date?
It's a solid estimate, but only about 5% of babies are born on their exact due date. A normal full-term birth can happen any time from 37 to 42 weeks. An early ultrasound (ideally before 13 weeks) gives the most reliable dating and may adjust this estimate.
What if my cycle is irregular?
If your cycles vary a lot, an LMP-based estimate is less reliable because ovulation timing is harder to predict. Enter your best average cycle length for a closer estimate, and confirm with your healthcare provider via ultrasound.

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