Pregnancy Due Date Calculator (EDD)
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.
Estimated Due Date (EDD) equals the first day of your last menstrual period (LMP) plus 280 days, or 40 weeks. This is Naegele's rule, the standard endorsed by ACOG. Example: an LMP on January 1 yields an EDD of October 8. Only about 4-5% of US babies arrive on the exact date; full-term delivery occurs between weeks 37 0/7 and 41 6/7. A first-trimester ultrasound (weeks 6-12) refines the EDD when cycles are irregular.
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).
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).
How it works
2 min read¿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:
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)
Key prenatal milestones by week
Sources & methodology
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.
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.