Which method should I use to estimate my due date?

If you know the first day of your last menstrual period (LMP) and have regular cycles, use LMP. If you know the exact conception date, use Conception. For IVF, use the transfer method. If a clinician measured gestational age by ultrasound, use the Ultrasound method.

How is due date calculated from LMP?

By Naegele’s rule: add 280 days to LMP. If your usual cycle length differs from 28 days, add or subtract the difference.

What cycle length should I enter?

Use your typical cycle length (e.g., 26–32 days). If unknown, 28 days is the standard assumption.

How is IVF due date calculated?

EDD = transfer date + (266 − embryo age in days). For day-3 embryos add 263 days; for day-5 embryos add 261 days.

Due Date Calculator

Q: How accurate is the due date?

Only about 4–5% give birth exactly on their due date. Most deliver within two weeks before or after. Early first-trimester ultrasounds generally provide the most accurate dating.

Q: Is this medical advice?

No. This tool is informational and does not replace guidance from your healthcare professional.

Data Source and Methodology

Authoritative sources:

American College of Obstetricians and Gynecologists (ACOG). Methods for Estimating the Due Date. Committee Opinion No. 700. First issued May 2017; reaffirmed 2024. Read the guidance.
NHS. Due Date Calculator. NHS Due Date Calculator.

All computations implement Naegele’s rule and ACOG-aligned ultrasound dating adjustments. All calculations are for education only and do not replace clinical judgment.

Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da questa fonte.

The Formula Explained

LMP method: EDD = LMP + 280\ \text{days} + (\text{CycleLength} - 28)\ \text{days}

Conception method: EDD = \text{ConceptionDate} + 266\ \text{days}

IVF method: EDD = \text{TransferDate} + (266 - \text{EmbryoAgeDays})\ \text{days}

Ultrasound method: EDD = \text{ScanDate} + \big(280 - (\text{GA}_w \times 7 + \text{GA}_d)\big)\ \text{days}

Glossary of Variables

LMP: First day of the last menstrual period.

CycleLength: Usual length of menstrual cycle in days; standard assumption is 28.

EDD: Estimated Due Date—40 weeks of gestation (280 days from LMP).

ConceptionDate: Ovulation/fertilization date (about 14 days after LMP in a 28-day cycle).

TransferDate: IVF embryo transfer date (day-3 or day-5 most common).

EmbryoAgeDays: Age of embryo at transfer in days (e.g., 3 or 5).

ScanDate: Date an ultrasound measured gestational age.

GA_w, GA_d: Gestational age at ultrasound in weeks and days.

How It Works: A Step-by-Step Example

Scenario: LMP on July 1, 2024, with a 30-day cycle.

Start with Naegele’s rule: add 280 days to LMP.
Adjust for cycle length: 30 − 28 = +2 days.
Total offset = 282 days.
EDD = 2024-07-01 + 282 days = April 9, 2025.

This matches the LMP formula: EDD = LMP + 280 + (30 - 28).

Frequently Asked Questions (FAQ)

Which method should I choose?

LMP is appropriate for regular cycles with a known start date. Use Conception if you know the exact ovulation date. For IVF, use the transfer method. If you have a first-trimester ultrasound, Ultrasound dating is typically most accurate.

How accurate is the due date?

Only a small percentage deliver exactly on the date. Most births occur within two weeks before or after. Ultrasounds in the first trimester offer the most precise dating.

Can I use this with irregular cycles?

Yes, but accuracy may be reduced. If cycles vary widely, an early ultrasound or clinician guidance is recommended.

What if my ultrasound date differs from LMP?

Clinicians often prioritize early ultrasound if discrepancy exceeds accepted thresholds (per ACOG criteria). Always follow your provider’s advice.

How do IVF day-3 vs day-5 transfers change EDD?

EDD = transfer date + (266 − embryo age in days). Day-3 → +263 days; Day-5 → +261 days.

Is this medical advice?

No—this is an educational estimate and not a substitute for professional medical advice.

Tool developed by Ugo Candido. Content verified by the CalcDomain Editorial Team.
Last reviewed for accuracy on: September 14, 2025.