What Does EDD Mean in Pregnancy?

EDD stands for “estimated due date”

The NHS calls the result of a due date calculation your estimated due date, or EDD.¹ You may also see it called the estimated date of delivery.⁴ Both describe the same thing: the date on which a pregnancy reaches 40 weeks 0 days, counted from the first day of the last period.²

The words that matter most are the first one and the last two. “Estimated” tells you it’s a calculated approximation. “Due date” tells you it marks the 40-week point — not the day labour is expected to start.

EDD vs “due date”: is there a difference?

No — they’re the same date. “Due date” is the everyday phrase; “EDD” is the abbreviation you’re more likely to see written down, where it stands for estimated due date¹ or estimated date of delivery.⁴ Whichever wording you see, it refers to 40 weeks 0 days.

How an EDD is worked out

• From your last period (LMP): by convention, the EDD is 280 days after the first day of the last menstrual period.²
• From an early scan: ultrasound measurement up to and including 13 weeks 6 days is the most accurate method to establish or confirm how far along a pregnancy is, and your healthcare team may set or adjust your EDD from it.²
• From an IVF transfer: the EDD is assigned from the embryo age and transfer date — 263 days after transfer for a day-3 embryo and 261 days for a day-5 embryo.²

You can calculate your estimated due date using your last period, a conception date or an IVF transfer date. The full method is explained in how a due date is calculated.

A worked example

Suppose the first day of your last period was 9 July 2026:

• EDD by LMP: 9 July 2026 + 280 days = 15 April 2027.²
• How far along on 4 October 2026: 87 days after the start of the period, which is 12 weeks 3 days.⁵
• Days to go on 4 October 2026: 193.

If an early scan later confirms these dates, the EDD stays 15 April 2027. If the scan differs by more than the threshold for that stage, guidance says the EDD should change to the scan date.²

“EDD by LMP” and “EDD by ultrasound”

If both a period date and a scan are available, you may come across two EDDs, labelled by how each was worked out:

• EDD by LMP — the date from your last period (280 days after its first day).²
• EDD by ultrasound — the date implied by an early scan.

They don’t always agree, because the LMP method assumes a regular 28-day cycle with ovulation on day 14.² ACOG guidance compares the two and changes the due date only when the difference is larger than a set number of days for that stage of pregnancy.² Once set, later changes should be reserved for rare circumstances.² Read more about ultrasound vs LMP dating.

How an EDD can be revised

1. A first EDD is usually worked out from your last period.²
2. An early scan — up to and including 13 weeks 6 days, the most accurate method to establish or confirm how far along you are — is compared with it.²
3. The EDD changes only if the two differ by more than the threshold for that stage: more than 5 days before 9 weeks 0 days, for example, or more than 7 days from 9 weeks 0 days to 13 weeks 6 days.²
4. After that, it should stay put: later changes should be reserved for rare circumstances.²

For IVF pregnancies, the EDD comes from the transfer date, and that ART-derived date should be used.²

Why the “estimated” matters

The LMP convention doesn’t account for irregular cycles or variable ovulation.² And pregnancy normally lasts from 37 to 42 weeks from the first day of the last period,¹ so the EDD marks 40 weeks, not the day labour will start.

In one Australian study, only 5% of births happened on the estimated date, and approximately 66% within 7 days of it.³ Read more about how accurate a due date is.

How to read your EDD

Think of your EDD as a reference point rather than an appointment:

• It tells you how far along you are. Because the EDD is 40 weeks 0 days, you can count back from it at any time — or find out how many weeks pregnant you are with the calculator.
• It anchors the term categories. ACOG’s full term runs from 39 weeks 0 days to 40 weeks 6 days, so your EDD sits inside full term.⁴
• It can be refined early on. An early scan may confirm or change it; after that, changes should be rare.²

Other pregnancy dating terms

Gestational age, completed weeks and day zero follow WHO definitions;⁵ the term categories are ACOG’s;⁴ the 40-week singleton average is from ACOG;⁴ ART dating follows ACOG guidance;² and preterm follows the WHO definition.⁶

Frequently asked questions

Is EDD the same as due date?

Yes. EDD is short for estimated due date — the term the NHS uses for the result of a due date calculation.¹

What does “EDD by LMP” mean?

The estimated due date worked out from your last menstrual period: 280 days after its first day.²

Is the EDD the same as 40 weeks?

Yes. The EDD is the day the pregnancy reaches 40 weeks 0 days, counted from the first day of the last period.²

Is the EDD the day my baby will be born?

Not necessarily. It marks 40 weeks 0 days, and in one study only 5% of births happened on the estimated date.³

Can my EDD change?

An early scan can confirm or change it. Once the EDD has been set from your last period and/or the first accurate ultrasound, later changes should be reserved for rare circumstances.²

How is an EDD worked out for IVF?

From the transfer date: 261 days after a day-5 embryo transfer or 263 days after a day-3 transfer.²

Medical statements in this article are linked to the numbered sources listed below: published clinical guidance and peer-reviewed research. It has not been reviewed by a named clinician. Read how content is written in our editorial policy, and see our medical disclaimer.