EDD Calculator — Naegele's Rule Due Date

First Day of Last Menstrual Period (LMP)

July 11th, 2026

This calculator uses Naegele's Rule only (LMP + 280 days / 40 weeks) — a fast, single-formula estimate. It does not adjust for cycle length or ultrasound dating.

Estimated Date of Delivery

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Select your LMP date above

Want cycle-length adjustment, current gestational progress, and a trimester progress bar? Use the fuller Pregnancy Due Date Calculator.

What is a EDD Calculator?

An EDD Calculator computes your Estimated Date of Delivery using Naegele's Rule, the classic obstetric formula of adding 280 days (40 weeks) to the first day of your last menstrual period. Developed by German obstetrician Franz Karl Naegele in the early 1800s, this remains the standard baseline method taught in obstetrics and used on virtually every pregnancy record today.

This calculator is deliberately built as a fast, single-formula tool: enter your LMP date, and get your EDD immediately, with no cycle-length adjustment or additional inputs. If you're specifically looking for the textbook Naegele's Rule answer, perhaps because you searched for "EDD calculator" directly, or need to double-check a due date mentioned on a medical record, this is the quickest way to get it.

For a fuller experience that adjusts for your actual average cycle length, shows a trimester progress bar, and tracks your gestational progress in more visual detail, see the site's Pregnancy Due Date Calculator. Both tools are accurate; they simply serve different needs, this one prioritizes speed and the pure formula, the other prioritizes a richer, adjustable experience.

This is informational and educational content only, not personalized medical advice. Your due date and pregnancy monitoring plan should always be confirmed and managed by your OB/GYN or midwife.

Why Use an EDD Calculator?

Sometimes you just need the number, a quick, no-frills answer to "what is 280 days from my last period?" without navigating extra sliders or settings. This calculator exists specifically for that use case: type in a date, get an EDD back instantly, using the exact formula that appears in virtually every obstetric textbook and prenatal record.

It's also useful as a quick verification tool, if a due date on a medical form or app doesn't match what you expected, running the pure Naegele's Rule calculation here can help you understand whether the discrepancy comes from a cycle-length adjustment, an ultrasound redating, or a data entry difference.

Who Should Use This Calculator?

Anyone who specifically wants the classic Naegele's Rule calculation, the exact LMP + 280 days formula, without additional adjustments or settings to configure.

People double-checking a due date from a medical record, app, or provider conversation, using this as a fast, independent verification against the standard formula.

Students and healthcare trainees learning Naegele's Rule as a foundational obstetric formula, using this calculator as a quick reference alongside textbook definitions.

Anyone in early pregnancy who wants a fast first estimate before their first prenatal appointment or dating ultrasound, understanding this baseline figure may later be refined by their provider.

What Insights Does This Calculator Give You?

Days Until EDD (the primary output) is the number of days remaining between today and your calculated due date.

Gestational Weeks (Today) and Extra Days show your current pregnancy progress in the familiar weeks-and-days format, calculated from your entered LMP to today's date.

Current Trimester indicates which of the three trimesters you're currently in, based on your gestational age today.

How to use this EDD Calculator calculator

Enter the first day of your last menstrual period using the date picker.
Read your Estimated Date of Delivery, the large date in the result card, calculated using Naegele's Rule.
Check your current Gestational Age and Trimester tiles for a quick snapshot of where you are in the pregnancy today.
Note the Days Until EDD figure for quick reference ahead of appointments or planning.
Use the Pregnancy Due Date Calculator if you want a cycle-length-adjusted estimate or a fuller trimester progress view.
Compare against ultrasound-based dating using the Crown-Rump Length Calculator if you've had a first-trimester dating scan, since your provider may use that instead if it differs meaningfully.

Show formula & methodology ↓Show less ↑

Formula & Methodology

Naegele's Rule
EDD = LMP + 280 days   (40 weeks)

Current Gestational Age
Days Pregnant = Today − LMP Weeks = floor(Days Pregnant ÷ 7) Extra Days = Days Pregnant mod 7

Trimester
Days Pregnant ≤ 91    → 1st Trimester Days Pregnant 92-182  → 2nd Trimester Days Pregnant > 182   → 3rd Trimester

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Worked Example:

A woman's last period started on March 1st.

| Variable | Value |
|---|---|
| LMP Date | March 1st |

EDD = March 1st + 280 days = December 5th

If today's date is May 10th, Days Pregnant = 70 days → 10 weeks, 0 days → 1st Trimester

Days Until EDD = 210 days

This quick Naegele's Rule estimate gives her an immediate due date to work with before her first prenatal appointment. She can cross-check it against the Pregnancy Due Date Calculator if her cycles run longer or shorter than 28 days, or against the Crown-Rump Length Calculator once she has a first-trimester dating ultrasound.

Frequently Asked Questions

What does EDD stand for?

EDD stands for Estimated Date of Delivery, the projected date your baby is due, calculated from the first day of your last menstrual period (LMP). It's the standard obstetric term used interchangeably with 'due date' on pregnancy records and ultrasound reports.

What is Naegele's Rule?

Naegele's Rule is the classic method for estimating a due date, developed by German obstetrician Franz Karl Naegele in the early 1800s: EDD equals the first day of your last menstrual period plus 280 days, which is 40 weeks. It assumes a standard 28-day cycle with ovulation occurring on day 14, and remains the most widely taught baseline method in obstetrics today.

How is this different from the Pregnancy Due Date Calculator?

This EDD Calculator is intentionally a fast, single-formula tool: it applies Naegele's Rule (LMP + 280 days) exactly, with no cycle-length adjustment. The Pregnancy Due Date Calculator on this site offers a fuller experience, including cycle-length adjustment, current gestational progress, and a trimester progress bar. Use this EDD Calculator when you specifically want the quick, textbook Naegele's Rule answer; use the fuller calculator for a richer, adjustable estimate.

Does Naegele's Rule account for irregular cycles?

No. Naegele's Rule assumes a standard 28-day cycle with ovulation on day 14. If your cycles are consistently longer or shorter than 28 days, your actual due date may differ from the pure Naegele's Rule estimate, the Pregnancy Due Date Calculator on this site includes a cycle-length adjustment for that situation.

Is my due date exact?

No due date calculation method, including Naegele's Rule, ultrasound dating, or IVF transfer dates, produces a guaranteed exact delivery day. Only about 5% of babies are actually born on their calculated due date; most arrive within a 2-week window around it. Due dates are best understood as a helpful estimate for care planning rather than a firm deadline.

Why do doctors sometimes adjust my due date after an ultrasound?

First-trimester ultrasound measurements, especially crown-rump length (see the Crown-Rump Length Calculator), are considered more accurate than LMP-based dating in many cases, since they measure the fetus directly rather than relying on cycle assumptions and recall of your last period date. If ultrasound dating differs meaningfully from your Naegele's Rule estimate, your provider may officially redate your pregnancy.

What if I don't remember my exact LMP date?

If you're unsure of your exact last period start date, your due date estimate from this calculator will carry that same uncertainty. An early ultrasound with crown-rump length measurement is generally the most reliable way to establish accurate dating when LMP recall is uncertain.

Can I use this calculator for twins or multiples?

Naegele's Rule itself doesn't distinguish between singleton and multiple pregnancies for the initial due date calculation, but pregnancies with twins or multiples are very commonly delivered before the calculated due date, and your provider will monitor and plan delivery timing based on your specific clinical situation rather than this general formula alone.

Does this calculator show my current pregnancy progress?

Yes, alongside your EDD, the calculator shows your current gestational age in weeks and days and which trimester you're in, calculated from today's date relative to your entered LMP.

How do I use the EDD Calculator?

Enter the first day of your last menstrual period using the date picker. The calculator instantly applies Naegele's Rule to show your Estimated Date of Delivery, your current gestational age, current trimester, and the number of days remaining until your due date.

Does this calculator store any of my personal information?

No. All calculations happen entirely within your browser. Your entered LMP date is never transmitted to or stored on any server, and everything is cleared when you close the page.

Also known as

EDD calculatorNaegele's rule calculatorestimated date of deliverydue date by LMP40 weeks from LMP calculator

EDD Calculator (Estimated Date of Delivery)