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Pregnancy Due Date Calculator

Estimate your due date and find out how many weeks pregnant you are today. Calculate from your last menstrual period, a known conception date, or an IVF embryo transfer — and see your trimester and estimated conception date.

Most cycles are 28 days. Adjust if yours differs.

Understanding the Pregnancy Due Date Calculator

The Pregnancy Due Date Calculator estimates your estimated due date (EDD) and tells you how far along you are right now. Pick how you want to calculate — from the first day of your last menstrual period (LMP), a known conception date, or an IVF embryo transfer (day 3 or day 5) — enter the date, and the tool returns your due date, current gestational age in weeks and days, your trimester, an estimated conception date, and how many days remain. For the LMP method you can set your average cycle length so the result adjusts if you ovulate earlier or later than average. Everything runs in your browser, and results are an estimate, not medical advice.

How it works

For the LMP method the tool applies Naegele’s rule: it adds 280 days (40 weeks) to the first day of your last period, then shifts the result by however many days your cycle differs from 28. Note that this 280-day count starts from the first day of your last period — not from conception, which happens roughly two weeks later — so the same calendar date entered as an LMP versus a conception date will give different results. A known conception date adds 266 days, because dating from conception skips the roughly two weeks before ovulation. IVF transfers are dated from the embryo’s age: a day-5 blastocyst adds 261 days and a day-3 embryo adds 263. To show how far along you are, the calculator derives an LMP-equivalent date, counts the days from then until today, and converts that to weeks plus days, a trimester, and the number of days left until your due date.

LMP method: Due date = LMP + 280 days + (cycle length − 28). Conception method: Due date = conception date + 266 days. IVF day-5 transfer: Due date = transfer date + 261 days. IVF day-3 transfer: Due date = transfer date + 263 days. Gestational age = (today − LMP-equivalent date), expressed as full weeks and remaining days; trimester 1 is weeks 0–12, trimester 2 weeks 13–26, trimester 3 weeks 27+.

Worked example

Suppose your last period started on January 1, 2026 and your cycle is 30 days (two days longer than average). The tool adds 280 days plus 2, giving a due date of October 10, 2026. It estimates conception around January 16, 2026 (day 14 plus the 2-day adjustment). If today is June 21, 2026, you are about 24 weeks and 3 days along — squarely in the second trimester — with roughly 111 days to go before your due date.

Tips & common mistakes

  • Use the first day of your last period, not the day it ended, for the LMP method.
  • If your cycles are not 28 days, enter your real average cycle length — it can move the due date by several days.
  • If you conceived through IVF, the transfer-date methods are more precise than LMP because the embryo’s age is known exactly.
  • A full-term birth is anywhere from 37 to 42 weeks, so treat the due date as the middle of a window, not a deadline.
  • Only about 5% of babies arrive on their exact due date — being early or late by a week or two is completely normal.
  • An early ultrasound is the most accurate way to date a pregnancy; your doctor or midwife may adjust your due date after a scan.

Sources & methodology

  • • ACOG (American College of Obstetricians and Gynecologists) – Methods for Estimating the Due Date
  • • Naegele’s rule for estimated date of delivery

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Reviewed by the TopOpenTools editorial team · Last updated June 2026. These tools provide general estimates for educational purposes only and are not financial, tax, insurance, investment, or medical advice. Verify important decisions with a qualified professional.

How to Use This Calculator

  1. 1Choose a method — last period, conception date, or IVF transfer.
  2. 2Enter the date (and your cycle length for the LMP method), then click Calculate Due Date.
  3. 3See your estimated due date, how far along you are, and your trimester — then confirm with your doctor.

Frequently Asked Questions

How is the due date calculated?

The classic method is Naegele’s rule: add 280 days (40 weeks) to the first day of your last menstrual period. From a known conception date we add 266 days instead, since pregnancy is about two weeks shorter than the LMP count.

What if my cycle is not 28 days?

Enter your average cycle length and the calculator adjusts automatically. A longer cycle means you ovulate later, so the due date shifts later by the same number of days your cycle exceeds 28 — and earlier for shorter cycles.

Will my baby arrive exactly on the due date?

Rarely — only about 5% of babies are born on their exact due date. A full-term birth is anything from 37 to 42 weeks, so think of the due date as the centre of a roughly five-week window rather than a deadline.