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Due Date Calculator

Find your estimated due date, how many weeks pregnant you are today, and your key dates, from your last period, conception, IVF or an ultrasound.

  • Free to use
  • No sign-up
  • Numbers stay in your browser

Last updated:

Calculate your due date

Count from the first day of bleeding.

days

The date starts as an example (14 weeks 3 days ago). Change it to yours, then press Calculate.

Your estimated due date

Enter your date and press Calculate to see your due date.

Pregnancy timeline

1st trimester
Weeks 1 to 13
Your baby's organs and body systems begin to form.
2nd trimester
Weeks 14 to 27
Your baby grows quickly.
3rd trimester
Weeks 28 to 40
Growth continues and your baby gets ready for birth.

Some health services count the trimesters a little differently (for example the second trimester from week 13). We use weeks 14 and 28.

What do LMP and EDD mean?

  • LMP is the first day of your last menstrual period. Doctors count the weeks of pregnancy from it.
  • EDD is the estimated due date: 40 weeks (280 days) after the LMP for a 28-day cycle.
  • Gestational age is how many weeks and days pregnant you are, counted from the LMP.

What is included

  • Due date from your last period, conception, IVF transfer, ultrasound or your due date
  • How many weeks and days pregnant you are today
  • Days to go and your trimester
  • Key dates and the term groups (early, full, late, post)
  • A pregnancy calendar, week by week
  • Free, with no sign-up

Important to know

This is an estimate, not medical advice. Only about 4 or 5 in 100 babies are born on the due date. Your midwife or doctor will confirm your dates, usually with an early scan. If you have any worries about your pregnancy, speak to them.

Use this free due date calculator, also called a pregnancy calculator, to find your estimated due date (EDD) and see how many weeks and days pregnant you are today. Choose how you want to date the pregnancy: the first day of your last period (LMP), your conception date, an IVF embryo transfer date, an ultrasound, or a due date you already know. You get your due date with the day of the week, the days to go, your trimester and a table of key dates, including the early term, full term, late term and post term groups. A pregnancy calendar lists the day you reach each week. It is free and instant, and your dates stay in your browser.

How a due date is worked out

Pregnancy usually lasts 280 days (40 weeks) counted from the first day of the last menstrual period (LMP), and the due date is the day that is 280 days after it. This is called Naegele's rule. Fertilisation usually happens about 14 days after the period starts, which is why the weeks of pregnancy are counted from the period and not from conception. Doctors call the date the EDD, the estimated due date. A pregnancy normally lasts from 37 to 42 weeks.

Last period: due date = LMP + 280 days (+ or − the days your cycle differs from 28)
Conception: due date = conception date + 266 days
IVF transfer: due date = transfer date + 266 days − the age of the embryo in days
Ultrasound: due date = scan date + (280 days − the pregnancy age on the scan)

From the first day of your last period

If your last period began on March 1, 2027 and your cycle is 28 days, the due date is December 6, 2027. If your cycle is longer or shorter than 28 days, the due date moves by the same number of days. With a 35-day cycle the same period gives December 13, 2027, because ovulation is likely a week later.

From the conception date

If you know the day you conceived, add 266 days (38 weeks). Conception on March 15, 2027 gives December 6, 2027, the same date as a period that began on March 1. The calculator also works backwards: enter a due date and it shows the estimated conception date and the first day of the last period.

After IVF

With IVF the date of fertilisation is known, so the estimate is usually more precise. The embryo is already a few days old when it is transferred, so the calculator takes the age of the embryo away from the 266 days: a day 5 embryo transferred on March 20, 2027 gives December 6, 2027 (March 20 + 261 days), and so does a day 3 embryo transferred on March 18 (March 18 + 263 days). Your clinic will tell you the age of your embryo.

From an ultrasound

A scan report gives the age of the pregnancy in weeks and days. If a scan on April 12, 2027 shows 8 weeks and 2 days, the due date is November 20, 2027. In the UK the midwife offers a scan at around 12 weeks that can estimate how many weeks pregnant you are more accurately. Your midwife or doctor decides whether to keep the date from your last period or change it to the date from a scan.

How many weeks pregnant am I?

Weeks and days pregnant are counted from the first day of the last period, not from conception. Someone who is 101 days from that date is 14 weeks and 3 days pregnant. The calculator reads today's date from your device and shows the weeks, the days to go and the trimester. The calendar by week lists the day you reach each week.

The three trimesters

  • First trimester: up to 13 weeks and 6 days.
  • Second trimester: 14 weeks to 27 weeks and 6 days.
  • Third trimester: from 28 weeks until the birth.

Some health services count the trimesters a little differently, for example the second trimester from week 13. The calculator uses weeks 14 and 28.

Early term, full term, late term and post term

The American College of Obstetricians and Gynecologists (ACOG) no longer calls the whole of weeks 37 to 42 “full term”. It uses four groups:

  • Early term: 37 weeks 0 days to 38 weeks 6 days.
  • Full term: 39 weeks 0 days to 40 weeks 6 days.
  • Late term: 41 weeks 0 days to 41 weeks 6 days.
  • Post term: 42 weeks and beyond.

How accurate is a due date?

A due date is a guide, not a promise. Only about 4 or 5 in 100 babies are born on it, and most arrive within a couple of weeks either side. Having your baby a little before or after the due date is common. Your midwife or doctor will confirm your date, usually with an early scan, and will talk to you about your own pregnancy. This calculator is not medical advice.

Sources

The rules, rates and ranges on this page come from these sources. Always check the current figures with the organization itself before you rely on them.

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Frequently Asked Questions

How is the due date calculated?

Pregnancy usually lasts 280 days (40 weeks) from the first day of the last menstrual period, so the due date is 280 days after it. A period that began on March 1, 2027 gives a due date of December 6, 2027. If your cycle is longer or shorter than 28 days, the date moves by the same number of days.

How accurate is a due date?

It is an estimate. Only about 4 or 5 in 100 babies are born on their due date, and most arrive between 37 and 42 weeks. Your midwife or doctor will confirm your date, usually with an early scan.

What if my cycle is shorter or longer than 28 days?

Enter your average cycle length on the Last period tab. The due date moves by the difference from 28 days. For a 35-day cycle it is 7 days later, so a period that began on March 1, 2027 gives December 13, 2027.

How do I work out my due date from the conception date?

Add 266 days (38 weeks) to the conception date. Conception on March 15, 2027 gives December 6, 2027. Use the Conception date tab and the calculator does the sum.

How do I work out my due date after IVF?

Use the IVF transfer tab and enter the transfer date and the age of the embryo (day 3 or day 5, for example). The due date is the transfer date plus 266 days minus the age of the embryo. A day 5 embryo transferred on March 20, 2027 gives December 6, 2027.

Can I use my ultrasound date?

Yes. On the Ultrasound tab enter the date of the scan and the weeks and days it shows. A scan on April 12, 2027 that shows 8 weeks 2 days gives a due date of November 20, 2027. Your midwife or doctor decides which date to use.

What does LMP mean? What does EDD mean?

LMP is the first day of your last menstrual period, which doctors use to count the weeks of pregnancy. EDD is the estimated due date, 40 weeks (280 days) after the LMP for a 28-day cycle.

How many weeks pregnant am I?

Weeks are counted from the first day of your last period. The calculator reads today's date from your device and shows how many weeks and days pregnant you are, how many days are left and your trimester.

What are the three trimesters?

The first trimester runs up to 13 weeks and 6 days, the second from 14 weeks to 27 weeks and 6 days, and the third from 28 weeks until the birth. Some health services count them a little differently, for example the second trimester from week 13.

When is a baby full term?

ACOG uses four groups: early term is 37 weeks 0 days to 38 weeks 6 days, full term is 39 weeks 0 days to 40 weeks 6 days, late term is 41 weeks 0 days to 41 weeks 6 days, and post term is 42 weeks and beyond.

Can the due date change?

Yes. Your midwife or doctor may change it after an early ultrasound, for example if the scan shows that the baby is bigger or smaller than expected for the date from your last period.

What if I do not remember my last period?

If you are not sure of the date, speak to a midwife or doctor. They can date the pregnancy with an ultrasound. If you know the conception date or had IVF, use those tabs instead.

Is this calculator a medical tool?

No. It gives an estimate from simple date maths and is not medical advice. Your midwife or doctor will confirm your due date and look after your pregnancy.

Can I save, share or print my results?

Yes. After you press Calculate, use Copy link to get a link that opens the calculator with the same dates, or Print for a clean printout. The dates sit after the # in the link, a part of the address that browsers do not send to our server.

Are my dates saved or shared?

No. The calculation happens in your browser, and the dates you type are not stored or sent to any server.