Pregnancy Due Date Calculator — Free EDD & Gestational Age Estimator

Guide

About the Pregnancy Due Date Calculator

Last updated: July 2026 · Reviewed by the NeftCal editorial team

The pregnancy due date calculator estimates your baby's estimated due date (EDD), current gestational age, and trimester using whichever dating information you have available — your last menstrual period (LMP), a known conception date, an IVF embryo transfer date, or an early ultrasound scan. It applies Naegele's Rule, the standard obstetric dating convention used by clinicians worldwide, and converts every method to an equivalent LMP internally so your results stay consistent no matter which one you choose. This due date calculator is a planning tool, not a diagnostic instrument — it complements, and never replaces, the dating your healthcare provider confirms during prenatal care.

What It Measures

This calculator measures three related things: your estimated due date (the calendar date 280 days, or 40 weeks, from the first day of your last menstrual period), your gestational age (how far along the pregnancy is, counted in completed weeks and days since LMP), and your trimester (1st, 2nd, 3rd, Full Term, or Post-Term, based on that same gestational-age count). It does not measure fetal size, weight, or development directly — those are assessed by a healthcare provider, typically via ultrasound.

Who Should Use This Calculator

This pregnancy calculator is designed for anyone who is pregnant or trying to understand pregnancy timing — expecting parents planning ahead, people cross-checking a date given at a doctor's visit, or anyone curious about gestational age math. It supports four separate entry points (LMP, conception, IVF transfer, ultrasound) so it's useful whether you conceived naturally, through fertility treatment, or simply know your due date from a scan and want to see the full milestone timeline that follows from it.

Why It Matters

Knowing your estimated due date, current pregnancy week, and trimester helps you plan prenatal appointments, anticipate key milestones like the anatomy scan or the viability threshold, and prepare for major life changes ahead of time. Since only around 5% of babies are born exactly on their due date, this calculator also shows a countdown and progress bar so you have a realistic window to plan around rather than treating one date as a certainty — a pattern consistent with how obstetric dating is used in real prenatal care.

Real-World Applications

Estimating a due date shortly after a positive pregnancy test, using LMP and Naegele's Rule
Cross-checking the due date a care provider gave you against an independent LMP or ultrasound-based estimate
Working out an accurate due date after IVF, using the exact known embryo transfer date
Tracking current gestational age and trimester week to week between prenatal visits
Planning ahead for the anatomy scan, viability milestone, or third-trimester appointments using the milestone timeline
Pairing with NeftCal's Conception Date Calculator and Pregnancy Weight Gain Calculator for a fuller pregnancy planning picture

Tips for Accurate Results

If your cycles are irregular or you're unsure of your LMP, switch to the Ultrasound or Conception Date method for a more reliable estimate
An early first-trimester ultrasound, ideally between 8–13 weeks, is generally considered the most accurate dating method since fetal size varies least at that stage
Enter your actual average cycle length rather than leaving the default 28 days if your cycles consistently run longer or shorter
If you conceived via IVF, use the IVF Transfer Date method with your exact transfer date rather than Naegele's Rule, since IVF timelines are known precisely
Treat the result as an estimate for planning purposes — your care provider's assessment, especially after an ultrasound, always takes precedence over any online pregnancy calculator

Formula

The Due Date Formula, Explained

Exactly how this calculator converts your dates into an estimated due date and gestational age

Naegele's Rule (LMP Method)

Estimated Due Date = First Day of LMP + 280 days, shifted by (Cycle Length − 28) days

Conception Date Method

Estimated Due Date = Conception Date + 266 days (equivalent LMP = Conception Date − 14 days)

IVF Transfer Date Method

Day 3 Transfer: EDD = Transfer Date + 263 days | Day 5 Transfer: EDD = Transfer Date + 261 days

Ultrasound Method

Estimated Due Date = Scan Date + (280 − Gestational Age at Scan, in days)

Every method above is converted internally into an equivalent last menstrual period (LMP) date. From that single reference point, the calculator computes gestational age as (today − equivalent LMP), trimester from completed gestational weeks, and the milestone timeline as fixed day-offsets from that same equivalent LMP — this is why gestational age and milestones stay consistent no matter which of the four methods you use.

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Naegele's Rule

The standard LMP-based estimate assumes a 28-day cycle with ovulation on day 14. This calculator adjusts for cycles other than 28 days by shifting the equivalent LMP by (cycle length − 28) days before adding 280 days.

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IVF Offsets (17 / 19 Days)

A Day 3 (cleavage-stage) embryo corresponds to 17 days post-LMP; a Day 5 (blastocyst) embryo corresponds to 19 days post-LMP. Subtracting these offsets from the transfer date back-calculates an equivalent LMP.

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Gestational Age & Trimester

Gestational age (days) = today − equivalent LMP. Trimester is read from completed weeks: under 13 weeks is 1st trimester, 13–27 is 2nd, 28–36 is 3rd, 37–41 is Full Term, and 42+ is Post-Term.

⚙️ Why This Formula Works

Naegele's Rule dates pregnancy from LMP rather than conception because LMP is a date most people can recall reliably, whereas the exact moment of conception usually isn't known. Since ovulation and conception typically occur around day 14 of an average cycle, adding 280 days (40 weeks) to LMP approximates 38 weeks of actual fetal development plus the roughly 2-week head start LMP dating carries — this convention has been used in obstetrics for close to two centuries and remains the basis for standard gestational-age counting today.

🎯 When to Use It

Getting a fast, standardized estimated due date from whichever dating information you already have
Tracking gestational age and trimester consistently across pregnancy
Previewing upcoming milestones like the anatomy scan or viability threshold

📋 Assumptions

Assumes ovulation occurs roughly mid-cycle (day 14 of a 28-day cycle, adjusted for other cycle lengths)
Assumes a single, average-length gestation of 280 days from LMP
Treats this as a standard obstetric dating convention, not an individualized medical prediction

⚠️ Limitations of the Formula

Cannot account for irregular ovulation timing beyond the cycle-length adjustment you provide
Assumes you recall your LMP date accurately, which isn't always the case
Uses population averages — actual gestation length varies naturally by several days to weeks between individuals
Cannot incorporate ultrasound measurements unless you select the Ultrasound method and enter them yourself

Walkthrough

Step-by-Step: How to Use the Pregnancy Due Date Calculator

From choosing a dating method to understanding your gestational age and milestones

Choose your calculation method

Select Last Menstrual Period (LMP), Conception Date, IVF Transfer Date, or Ultrasound Date, depending on which information you know most reliably.

Enter your date information

Type in the relevant date — your LMP, conception date, embryo transfer date, or ultrasound scan date — into the field that appears for your chosen method.

Adjust cycle length or scan details if applicable

For the LMP method, enter your average cycle length if it isn't 28 days. For IVF, select Day 3 or Day 5 transfer. For ultrasound, enter the gestational age shown on your scan report.

Click "Calculate Due Date"

The calculator converts your chosen method into an equivalent last menstrual period date internally, then applies Naegele's Rule (adds 280 days) to estimate your due date.

Review your due date, gestational age, and milestone timeline

See your estimated due date, current gestational age, trimester, days remaining, pregnancy progress bar, and a full timeline of key pregnancy milestones with two visual charts.

Example

Worked Example

Using the LMP method with a default 28-day cycle

Scenario

Suppose the first day of your last menstrual period was March 1, 2026, and your average cycle length is the default 28 days. Checking gestational age as of July 22, 2026.

LMP DateMarch 1, 2026

Cycle Length28 days (default)

Check DateJuly 22, 2026

Step 1 — Adjust LMP for cycle length: Shift = Cycle Length − 28 = 28 − 28 = 0 days, so the equivalent LMP stays March 1, 2026.

Step 2 — Apply Naegele's Rule: Due Date = March 1, 2026 + 280 days = December 6, 2026.

Step 3 — Estimate conception date: Conception ≈ equivalent LMP + 14 days = March 1 + 14 = March 15, 2026.

Step 4 — Compute gestational age as of July 22, 2026: Days elapsed = March 1 → July 22 = 143 days = 20 weeks 3 days (143 ÷ 7 = 20 remainder 3), which falls in the 13–27 week range, so the trimester shown is 2nd Trimester.

Step 5 — Days remaining and progress: Days To Go = Due Date − Check Date = December 6 − July 22 = 137 days. Progress = 143 ÷ 280 × 100 ≈ 51% of the way through the pregnancy.

Due Date

Dec 6, 2026

Gestational Age

20w 3d

Trimester

2nd Trimester

Explanation: With a standard 28-day cycle, no shift is needed and Naegele's Rule applies directly — 280 days after LMP. At the check date of July 22, 2026, this scenario sits just past the halfway point (51%) of pregnancy, squarely in the 2nd trimester, with the anatomy scan milestone (week 20) already behind it and roughly 137 days — about 19-20 weeks — remaining until the due date. As with any due date estimate, this is a planning figure: actual delivery could reasonably occur anywhere from a few weeks before to a couple of weeks after December 6.

Interpretation

Understanding Your Gestational Age and Trimester

What each stage of the pregnancy timeline generally means

Gestational Age	Stage	What It Generally Means
0 – 12 weeks	1st Trimester	Early development stage; first prenatal visit and initial screening typically occur here
13 – 27 weeks	2nd Trimester	Often called the most comfortable stage; anatomy scan and viability milestone fall in this window
28 – 36 weeks	3rd Trimester	Final growth phase; prenatal visits typically become more frequent
37 – 41 weeks	Full Term	Standard delivery window; babies born in this range generally have the best average outcomes
42+ weeks	Post-Term	Beyond the typical full-term window; care providers often discuss monitoring or induction options

If your gestational age falls in the 1st or 2nd trimester: this is typically a time for routine prenatal visits, screening tests, and the anatomy scan — the due date shown is a distant planning marker rather than an imminent one.

If your gestational age falls in the 3rd trimester or later: the due date and milestone countdown become more immediately relevant for planning delivery logistics, though remember that anywhere from 37 to 42 weeks is considered a normal, full-term delivery window.

This result is for informational purposes only and is not a medical diagnosis. Gestational age and due date estimates are based on standard obstetric dating conventions, not an individualized assessment of your pregnancy — only about 5% of babies are born on their exact estimated due date, and a healthcare provider's ultrasound-based dating is generally more precise than an LMP-based estimate like this one.

ℹ️

This calculator provides educational estimates only and should not be used as a substitute for professional medical advice, diagnosis, or treatment. Results may vary depending on individual health conditions. Always consult a qualified healthcare professional regarding medical concerns.

Use Cases

Practical Use Cases for the Pregnancy Due Date Calculator

Where a fast, private due date and gestational age estimate is genuinely useful

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Estimating a due date after a positive test

Get an immediate EDD estimate from your LMP using Naegele's Rule before your first prenatal visit.

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Preparing for your first prenatal appointment

Arrive with an estimated due date and gestational age already calculated to discuss with your provider.

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IVF pregnancy dating

Use the exact known embryo transfer date for a due date estimate that doesn't rely on assumed ovulation timing.

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Cross-checking an ultrasound due date

Compare the due date your care provider gave you against an independent LMP or ultrasound-based calculation.

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Planning around key milestones

See upcoming dates for the anatomy scan, viability milestone, and third-trimester start to plan appointments and travel.

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Sharing pregnancy news with family

Get a clear estimated due date and trimester to share, along with a countdown of days remaining.

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Planning parental leave timing

Use the estimated due date as a starting reference point when discussing leave dates with an employer.

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Understanding gestational age terminology

See exactly how "weeks pregnant" is calculated from LMP, useful when reading prenatal test results.

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Recalculating after a revised due date

Re-run the calculator with an ultrasound-based date if your provider adjusts your original LMP estimate.

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Health education and coursework

Students and educators can use it to illustrate Naegele's Rule and gestational age calculations.

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Method-flexible dating

Switch freely between LMP, conception, IVF, and ultrasound methods depending on what information is available.

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Setting a realistic delivery window

Use the full-term range (37–42 weeks) shown in the interpretation table to set expectations, not a single fixed day.

Pros & Cons

Benefits and Limitations

What this pregnancy due date calculator does well, and where it can't replace professional prenatal care

✅ Benefits

Free, instant, and requires no signup or personal information
Runs entirely in your browser — your dates are never sent to a server
Supports four dating methods (LMP, conception, IVF, ultrasound) in one tool
Uses the standard obstetric convention, Naegele's Rule, for LMP-based dating
Adjusts automatically for cycle lengths other than 28 days
Gives IVF-specific offsets for Day 3 and Day 5 embryo transfers
Shows gestational age, trimester, and days-to-go together, not just a due date
Includes a full milestone timeline (missed period through due date)
Visual progress bar and charts make results easy to interpret at a glance
Flags unusual inputs, like a future LMP or an extreme gestational age, with a warning
Downloadable plain-text summary of your results
Fast-loading and mobile-friendly
Based on a publicly documented, widely used obstetric dating formula

⚠️ Limitations

Irregular cycles reduce the accuracy of LMP-based estimates, even with the cycle-length adjustment
Assumes you recall your LMP or conception date accurately, which isn't always possible
Cannot incorporate an ultrasound measurement unless you manually select that method and enter it
Uses population-average gestation length (280 days); actual gestation varies naturally between individuals
Not a substitute for a prenatal care provider's dating — especially an early ultrasound, which is generally more precise than LMP-based estimates
Cannot detect or assess pregnancy complications, fetal health, or growth
A single calculated date is a snapshot estimate, not a certainty — only about 5% of babies arrive exactly on their due date
Does not account for multiples (twins, triplets), which are commonly delivered earlier than singleton pregnancies
Not intended to replace regular prenatal checkups or professional monitoring

Reference

LMP vs. Conception vs. Ultrasound Dating

How the three main pregnancy dating methods compare

Method	What It Uses	Typical Reliability
LMP (Naegele's Rule)	First day of last menstrual period + cycle length	Good starting estimate; less reliable with irregular cycles or uncertain LMP recall
Conception Date	Known or estimated date of conception	Reliable only if the conception date is genuinely known (e.g. single-cycle tracking, IUI)
IVF Transfer Date	Exact embryo transfer date and transfer day (3 or 5)	Very reliable — timeline is precisely known, no ovulation-timing assumption needed
Ultrasound (1st trimester)	Fetal measurements at 8–13 weeks	Generally the most accurate method overall, per standard obstetric guidance

Common Mistakes and Expert Tips

❌ Common Mistakes

Using Naegele's Rule with a known-inaccurate LMP date instead of switching to conception or ultrasound dating
Leaving the cycle length at the default 28 days despite consistently having longer or shorter cycles
Assuming an IVF due date follows Naegele's Rule instead of using the IVF-specific transfer-date offsets
Treating a single calculated due date as a guaranteed delivery date rather than a planning window
Confusing gestational age (from LMP) with fetal age (from conception), which run about two weeks apart
Ignoring a due date revision from an early ultrasound in favor of the original LMP-based estimate

💡 Expert Tips & Best Practices

Use the Ultrasound method once you have a first-trimester scan — it's generally the most accurate input available
Recalculate after any provider-confirmed date revision so your gestational age and milestones stay accurate
Pair this calculator with the Conception Date Calculator to cross-check estimates from a different angle
If you conceived via IVF, always use your exact transfer date rather than an LMP-based guess
Treat the due date as the center of a normal range (37–42 weeks), not a single fixed appointment

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Summary: This pregnancy due date calculator gives you an instant, free estimate of your due date, gestational age, and trimester from LMP, conception, IVF transfer, or ultrasound dates, using Naegele's Rule and related obstetric conventions — a useful planning tool, not a medical diagnosis. Pair it with related tools like the Conception Date Calculator, Ovulation Calculator, and Pregnancy Weight Gain Calculator for a fuller picture of your pregnancy timeline.

FAQ

Frequently Asked Questions

Common questions about due date and gestational age calculations

How accurate is a pregnancy due date calculator?

A pregnancy due date calculator provides an estimate, not a guarantee — only around 5% of babies are born on their exact due date. Most babies arrive within a week or two of the estimate, and a full-term pregnancy can end anywhere from 37 to 42 weeks. A due date confirmed by an early first-trimester ultrasound is generally considered the most accurate, since fetal size varies least at that stage. Always treat the calculator's result as a planning estimate, not a medical prediction.

What's the difference between gestational age and fetal age?

Gestational age is counted from the first day of your last menstrual period (LMP), even though conception happens roughly two weeks later. Fetal, or conceptional, age is counted from the actual date of conception, so it runs about two weeks behind gestational age. Doctors, midwives, and this calculator all use gestational age as the standard measure of how far along a pregnancy is, since LMP is usually easier to identify than the exact conception date.

Can my due date change during pregnancy?

Yes. If an early ultrasound measurement differs meaningfully from the LMP-based estimate, a care provider may revise the due date — typically only if the difference is more than 5 to 7 days in the first trimester. Once a due date is set from a reliable early scan, it is rarely changed again later in pregnancy, since first-trimester ultrasound dating is considered the most reliable method available.

What if I don't know my LMP or have irregular cycles?

If your cycles are irregular or you're unsure of your last menstrual period date, switch this calculator to the Conception Date or Ultrasound method instead. An ultrasound dating scan, ideally performed between 8 and 13 weeks, is the most reliable way to establish gestational age when LMP is uncertain, since it measures the fetus directly rather than relying on cycle assumptions.

What calculation methods does this due date calculator support?

Four methods: Last Menstrual Period using Naegele's Rule (LMP + 280 days, adjusted for cycle length), Conception Date (conception + 266 days), IVF Transfer Date (transfer date + 263 days for a Day 3 transfer or + 261 days for a Day 5 transfer), and Ultrasound Date (scan date plus the remaining days needed to reach 280, based on the gestational age recorded at the scan).

How is the due date calculated from an IVF embryo transfer date?

A Day 3 (cleavage-stage) embryo transfer corresponds to 17 days after LMP, so the due date is Transfer Date + 263 days. A Day 5 (blastocyst) embryo transfer corresponds to 19 days after LMP, so the due date is Transfer Date + 261 days. These offsets back-calculate an equivalent LMP date so gestational age and milestones stay consistent with the other dating methods.

What is Naegele's Rule?

Naegele's Rule is the standard obstetric formula for estimating a due date: take the first day of the last menstrual period and add 280 days (40 weeks). It assumes a 28-day cycle with ovulation on day 14. This calculator adjusts the estimate automatically when you enter a cycle length other than 28 days, shifting the estimated ovulation day accordingly.

How many weeks is a full-term pregnancy?

A pregnancy is generally considered full term between 39 and 40 completed weeks of gestational age. Medical organizations further break this down into early term (37–38 weeks), full term (39–40 weeks), late term (41 weeks), and post-term (42 weeks and beyond). Babies born across the full-term window tend to have the best average health outcomes, though every pregnancy is different.

What do early term, full term, late term, and post-term mean?

These are standard labels for when birth occurs relative to the estimated due date. Preterm is before 37 weeks, early term is 37–38 weeks, full term is 39–40 weeks, late term is 41 weeks, and post-term is 42 weeks or beyond. This calculator's trimester field shows "Full Term" once gestational age reaches 37 completed weeks and "Post-Term" at 42 weeks.

Can I use this calculator if I conceived through IVF?

Yes. Select the IVF Transfer Date method, enter your embryo transfer date, and choose whether it was a Day 3 or Day 5 transfer. Because IVF timelines are known precisely, this method is generally more reliable than Naegele's Rule for IVF pregnancies, which assumes a natural conception timeline that doesn't apply to a transferred embryo.

Why does the calculator ask for my average cycle length?

Naegele's Rule assumes a 28-day cycle with ovulation on day 14. If your average cycle is longer or shorter, ovulation — and therefore conception — likely happened on a different day relative to your LMP. Entering your actual average cycle length lets the calculator shift the estimated due date earlier or later to better reflect your typical cycle.

Is ultrasound dating more accurate than LMP dating?

For most pregnancies, yes — a first-trimester ultrasound (ideally 8–13 weeks) is generally considered more accurate than LMP-based dating, since it measures the fetus directly and doesn't depend on remembering LMP correctly or assuming a textbook 28-day cycle with day-14 ovulation. LMP dating remains useful as a first estimate, especially before an ultrasound has been performed.

What does the warning message in the calculator mean?

The calculator shows a warning if your inputs produce a last menstrual period date in the future, or a gestational age well beyond a full-term pregnancy (over roughly 300 days). Both situations usually indicate a mistyped date rather than an actual medical finding — double-check the date you entered and your calculation method.

How is gestational age different from how many weeks pregnant I am?

They're the same measure. "How many weeks pregnant" is the everyday way of describing gestational age — the time elapsed since the first day of your last menstrual period, expressed in completed weeks and days. This calculator shows both the gestational age (e.g. "20w 3d") and the corresponding trimester based on that same count.

Does this calculator diagnose pregnancy complications?

No. This calculator only estimates dates — due date, gestational age, and trimester — based on standard obstetric dating conventions. It cannot detect, diagnose, or rule out any pregnancy complication. Any concerns about symptoms, bleeding, pain, or fetal development should be discussed directly with a qualified healthcare provider, not inferred from a dating calculator.

Is this pregnancy due date calculator free and private to use?

Yes. This calculator is completely free, requires no signup or account creation, and runs entirely in your browser — the dates you enter are never transmitted to or stored on a server. You can use it as many times as you like, switching between LMP, conception, IVF, and ultrasound dating methods.