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Pregnancy Due Date Calculator (EDD)

Calculate your estimated due date (EDD) in seconds using your last menstrual period (LMP). Get gestational week, trimester, and days remaining with Naegele's…

Data verified · June 2026
Edited by Martín Rodríguez
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Edited by: Martín Rodríguez (editorial policy ) · Last editorial review: Jun 19, 2026

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When to Take a Pregnancy Test: Reliable ResultsEnter your last period to find the earliest reliable day for blood or urine testing. Avoid false negatives.Due Date by Conception Date CalculatorCalculate estimated due date from conception or ovulation date. Compare conception-based dating (266 days) vs LMP method for accurate pregnancy timeline.Pregnancy Calendar Week-by-WeekCalculate your pregnancy timeline week-by-week with baby size milestones, trimester boundaries, and key prenatal screening appointments from LMP or due date.Conception Date CalculatorCalculate your estimated conception date from your due date or LMP. Find your fertile window (5-day range) and current gestational age in weeks.

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How to use this calculator

Follow this tool’s steps, then review its formula, assumptions, and limits below.

Step by step

Enter your LMP dateSelect the first day of your last menstrual period. This is day 1 of week 1.

Read your estimated due dateThe primary result is your EDD — when your baby is expected to be born (LMP + 280 days).

Check your current week and trimesterThe calculator also shows how many weeks pregnant you are today, which trimester, and days until delivery.

Calculate your estimated due date (EDD) from the first day of your last menstrual period (LMP) — the same method US OB-GYNs use at your first prenatal visit. This free pregnancy due date calculator applies Naegele's rule (the standard endorsed by ACOG and used across US obstetrics) to add 280 days (40 weeks) to your LMP and returns your expected delivery date in MM/DD/YYYY format, current gestational week, trimester, and days remaining. Aligned with CDC pregnancy guidance and the ACOG Committee Opinion 700 on EDD methodology, this tool gives you a fast, doctor-style estimate while you wait for your dating ultrasound.

When to use this calculator

Your first question after a positive pregnancy test: "when is my baby due?"
You need the EDD to plan maternity leave and work handover.
You want to know how many weeks pregnant you are today and when each trimester starts.
Planning prenatal appointments: the 20-week anatomy scan, glucose test, dTpa vaccine.
Predicting which week you'll enter the "full-term" window (week 37).

Gestational age categories and delivery windows (ACOG)

Category	Gestational age	What it means
Preterm	Before 37 0/7 weeks	Born early; may need NICU monitoring
Early term	37 0/7 – 38 6/7 weeks	Full-term range begins
Full term	39 0/7 – 40 6/7 weeks	Ideal delivery window (EDD = 40 0/7)
Late term	41 0/7 – 41 6/7 weeks	Closer monitoring of mother and baby
Post-term	42 0/7 weeks and beyond	Induction usually recommended

Source: ACOG (2026). EDD = LMP + 280 days (40 weeks). Only about 4–5% of US babies are born on the exact due date; roughly 80% of deliveries occur between weeks 37 and 41, most often in week 39.

How it works

¿Qué es la fecha probable de parto (EDD)?

La fecha probable de parto (EDD, por sus siglas en inglés) es la fecha estimada en que nacerá tu bebé, calculada sumando 280 días (40 semanas) al primer día de tu último período menstrual. Se basa en la regla de Naegele, el estándar de oro en obstetricia. Solo el 5% de los bebés nacen exactamente en la EDD; un parto a término ocurre entre las semanas 37 y 42.

What is the Estimated Due Date (EDD)?

The Estimated Due Date (EDD) — also called Expected Date of Delivery (EDD) or Estimated Date of Confinement (EDC) — is the date your baby is expected to be born, calculated as 40 weeks (280 days) after the first day of your last menstrual period (LMP).

This is called Naegele's rule, developed by German obstetrician Franz Karl Naegele in 1812 and still the worldwide standard.

Formula: EDD = LMP + 280 days (or equivalently: LMP − 3 months + 7 days + 1 year).

How accurate is a due date calculator?

A calculator based on LMP is accurate when cycles are regular (28 days). Accuracy drops when:

Cycles are irregular or longer/shorter than 28 days.

You don't remember the exact first day of your last period.

Ovulation was late or early.

The most accurate way to date a pregnancy is a first-trimester ultrasound (weeks 6–12), which measures the crown-rump length (CRL). If the ultrasound EDD differs from the LMP EDD by more than 7 days in the first trimester (or 10+ days in the second), obstetricians typically switch to the ultrasound date.

Only 5% of babies are born on their exact due date

Terminology matters:

Category	Weeks	Notes
Preterm	Before 37	Requires NICU monitoring
Early term	37 0/7 – 38 6/7	Full-term range begins
Full term	39 0/7 – 40 6/7	Ideal delivery window
Late term	41 0/7 – 41 6/7	Closer monitoring
Post-term	42+	Induction usually recommended

Only about 5% of babies arrive exactly on the EDD. ~80% of deliveries happen between week 37 and 41, most commonly in week 39.

Trimesters (ACOG definition)

1st trimester: weeks 1–13

2nd trimester: weeks 14–27

3rd trimester: weeks 28 onward

Key prenatal milestones by week

Week 6–7: First heartbeat visible on ultrasound.

Week 10–13: Nuchal translucency scan (Down syndrome screening).

Week 20: Anatomy scan (Level II ultrasound) — detects structural anomalies and usually reveals the baby's sex.

Week 24–28: Glucose challenge test (O'Sullivan) for gestational diabetes.

Week 27–28: Tdap (dTpa) vaccine — whooping cough protection for the baby.

Week 35–37: Group B Strep (GBS) swab.

Week 37: Full-term window opens.

Week 40: Due date.

Sources & methodology

American College of Obstetricians and Gynecologists (ACOG)

World Health Organization — Maternal health

Mayo Clinic — Fetal development timeline

ACOG Committee Opinion 700: Methods for Estimating the Due Date (2017).

Disclaimer

This calculator provides an estimate based on self-reported LMP and should not replace a medical consultation. Always confirm your due date with a healthcare provider and a first-trimester ultrasound.

Example: LMP was January 1, 2026

LMP: January 1, 2026.

Due date formula: LMP + 280 days.

280 days after Jan 1 = October 8, 2026.

Today is April 22 → 111 days since LMP = 15 weeks and 6 days pregnant.

Trimester: 2nd (weeks 14–27).

Days until due: 280 − 111 = 169 days (about 24 more weeks).

Estimated due date: 10/08/2026. Currently 15 weeks, 6 days pregnant — 2nd trimester.

Frequently asked questions

How do I calculate my due date?

Add 280 days (40 weeks) to the first day of your last menstrual period. Example: LMP on January 1 → due date October 8 of the same year. This calculator does the math automatically using Naegele's rule.

What is an EDD calculator?

EDD stands for Estimated Due Date. An EDD calculator takes your LMP (last menstrual period) and returns the date your baby is estimated to arrive (LMP + 280 days), plus your current week, trimester, and days remaining.

How accurate is the due date from LMP?

Very accurate when you know your LMP and your cycles are regular (28 days). Accuracy drops with irregular cycles. A first-trimester ultrasound is the most precise way to date a pregnancy and may adjust your EDD by a few days.

What if I don't remember my LMP?

Ask your doctor for a dating ultrasound (best between weeks 6 and 12). It measures the embryo's crown-rump length and produces a reliable EDD even without a known LMP.

Will my baby come on the due date?

Probably not. Only about 5% of babies are born exactly on their due date. Normal range is week 37 to week 42. Most deliveries cluster around week 39–40.

What's the difference between EDD, EDC and expected date of delivery?

All three are the same thing: the estimated day your baby is expected to be born. EDD = Estimated Due Date, EDC = Estimated Date of Confinement (older term), and "Expected Date of Delivery" is the plain-English version.

Can I use this calculator if I know my conception date instead of LMP?

If you know the conception date, add 266 days (38 weeks) to get the EDD — conception typically occurs about 2 weeks after LMP. Or enter an LMP 14 days earlier than your conception date for the same result in this calculator.

When does the third trimester start?

The third trimester starts at week 28 and continues through delivery. It's the final stretch, with more frequent appointments, growth monitoring, and birth preparation.

Is this due date calculator free?

Yes — 100% free, no signup, no ads interfering with your result. Just enter your LMP and get the EDD instantly.

Sources & references

Methodology & trust

Editorial

Health calculator with its formula verified automatically against CDC — Pregnancy: During Pregnancy, per our editorial policy and methodology.

Updates

Updated: June 19, 2026. Parameters are verified periodically against the cited sources.

Privacy

Calculations run 100% in your browser. We do not store or transmit your data.

Limitations

Indicative results. For critical decisions, consult a professional.

📌 How to cite this calculator

Rodríguez, M. (2026). Pregnancy Due Date Calculator (EDD). Hacé Cuentas. https://hacecuentas.com/en/pregnancy-due-date-calculator

Content licensed under CC-BY 4.0 — reuse it citing the source with a link to Hacé Cuentas.

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