# Due Date Calculator

> Estimate your due date from your last period, a known conception date, a day-3 or day-5 IVF embryo transfer, or an ultrasound scan, using ACOG conventions.

Category: Health & fitness · Applies to: Worldwide · Last updated: 2026-10-29
Interactive calculator: https://calculators.geekmidst.com/calculators/due-date-calculator

A due date is 280 days after the first day of the last period, 266 days after conception, or 261 or 263 days after a day-5 or day-3 IVF embryo transfer.

Also called: EDD calculator, Pregnancy due date calculator, IVF due date calculator.

## Inputs
- Calculate from (options: First day of last period, Conception date, IVF embryo transfer, Ultrasound scan; default lmp)
- First day of last period (default 2026-05-01)
- Usual cycle length (unit days; default 28; optional)
- Conception date (default 2026-05-15)
- Embryo transfer date (default 2026-05-20)
- Embryo age at transfer (options: Day 5 (blastocyst), Day 3; default 5)
- Scan date (default 2026-07-01)
- Gestational age at scan (weeks) (unit weeks; default 12)
- Plus days (unit days; default 0; optional)

## Results
- Estimated due date
- Term window (37 weeks to 41 weeks 6 days)
- Pregnancy dated from (LMP equivalent)
- Estimated conception

## Formula

```
LMP: due = LMP + (cycle − 28) + 280;  Conception: due = conception + 266;  IVF day 5: transfer + 261;  IVF day 3: transfer + 263;  Scan: due = scan date + 280 − gestational age at scan (days)
```

Where:
- LMP: first day of last period
- 280 days: 40 weeks
- gestational age at scan: weeks × 7 + days, as measured by ultrasound

## Worked example
1. Last period started 1 March 2026 and the cycle is 28 days, so no adjustment is needed.
2. Due date = 1 March 2026 + 280 days = 6 December 2026.
3. Term runs from 37 weeks (+259 days, 15 November) to 41 weeks 6 days (+293 days, 19 December).

**Result:** A last period starting on 1 March 2026 gives an estimated due date of Sunday 6 December 2026.

## What the result means

IVF dates are the most precise because the embryo’s age is known. Otherwise, a first-trimester scan is more accurate than period dates, and your care team will normally use it to confirm or change the due date.

## Assumptions and limits
- Conventions from ACOG Committee Opinion 700: 280 days from LMP; 261 days from a day-5 and 263 days from a day-3 embryo transfer.
- Conception taken as 14 days after the (cycle-adjusted) LMP, 266 days before the due date.
- Period-based dates assume regular cycles with ovulation 14 days before the next period.
- The scan method assumes the gestational age you enter is the one reported on your scan.

## Questions

### What is Naegele’s rule?

It is a shortcut for the same calculation: take the first day of the last period, subtract three months and add seven days (and a year where needed).

### Why does a day-5 transfer use 261 days?

A day-5 embryo is already 5 days past fertilisation, and fertilisation corresponds to 2 weeks of gestational age, so 280 − 14 − 5 = 261 days remain.

## Sources
- [ACOG Committee Opinion 700: Methods for Estimating the Due Date (2017)](https://www.healthcare.uiowa.edu/familymedicine/fpinfo/OB/OB2017/ACOG%20redating%20gestational%20age.pdf)
- [StatPearls: Estimated Date of Delivery](https://www.statpearls.com/ArticleLibrary/viewarticle/21375)

## Related calculators
- [Pregnancy Calculator](https://calculators.geekmidst.com/calculators/pregnancy-calculator)
- [Pregnancy Conception Calculator](https://calculators.geekmidst.com/calculators/pregnancy-conception-calculator)
- [Pregnancy Weight Gain Calculator](https://calculators.geekmidst.com/calculators/pregnancy-weight-gain-calculator)
- [Date Difference Calculator](https://calculators.geekmidst.com/calculators/date-difference-calculator)

_This is a general screening estimate for adults, not medical advice or a diagnosis. Talk to a qualified health professional about your health._

Source: GM¹X CalcVerse — https://calculators.geekmidst.com/calculators/due-date-calculator