Pregnancy Due Date Calculator | Calculate EDD, Gestational Age & Trimesters | Numovix

INTRODUCTION

You missed your period.

The test showed two lines.

Your heart raced. Your hands shook. Your life changed in sixty seconds.

Now every question feels urgent.

"When am I due?"

"How far along am I?"

"When will I feel the first kick?"

"When is the baby actually coming?"

You call your doctor. They ask: "When was the first day of your last menstrual period?"

You freeze. Was it March 14? March 18? You are not sure.

They give you a date. December 21.

But you have irregular cycles. Sometimes 28 days. Sometimes 35.

That date could be off by two weeks.

Two weeks matters.

It matters for when you hear the heartbeat.

It matters for the anatomy scan at 20 weeks.

It matters for the glucose test at 24–28 weeks.

It matters for knowing when you reach viability at 24 weeks.

It matters for your maternity leave paperwork.

It matters for when you pack the hospital bag.

And here is the truth almost no first-time parent knows:

Only 4–5% of babies are born on their exact due date.

The due date is not a deadline. It is a reference point. A middle of a five-week window.

But without that reference point, you are navigating pregnancy blind.

A Pregnancy Due Date Calculator gives you that reference point.

It calculates your EDD (Estimated Due Date) from your LMP, conception date, IVF transfer date, or early ultrasound.

It tells you what trimester you are in.

It tells you your gestational age in weeks and days.

It tells you when major milestones happen.

In 2026, with pregnancy apps everywhere but clarity rare, having an accurate, simple due date calculator is not a luxury.

It is essential for every expecting parent.

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WHAT IS A PREGNANCY DUE DATE CALCULATOR?

A pregnancy due date calculator is a tool that estimates when your baby will arrive based on pregnancy dating science.

It uses multiple methods because pregnancy is not one-size-fits-all:

• LMP Method (Naegele's Rule) — Most common. Uses first day of last menstrual period.

• Conception Date Method — If you know the exact date of conception (natural or fertility treatment).

• IVF Method — Uses embryo transfer date and age of embryo at transfer.

• Ultrasound Method — Uses crown-rump length from first-trimester ultrasound, the most accurate dating method clinically.

• Cycle Length Adjustment — Adjusts Naegele's Rule for cycles longer or shorter than 28 days.

Standard inputs:

• First day of last menstrual period (LMP)

• Average cycle length (default 28 days, adjustable)

• Conception date (if known)

• IVF embryo transfer date (and embryo age: day 3 or day 5)

• Ultrasound date and gestational age at time of scan

• Date of first positive pregnancy test (optional, rough estimate)

Outputs you get:

• Estimated Due Date (EDD) — Your primary reference date

• Gestational age — How many weeks and days pregnant you are today

• Fetal age — Developmental age (2 weeks less than gestational age)

• Trimester — First, second, or third

• Days remaining until due date

• Conception window — Estimated range of fertilization

• Implantation window — When embryo likely implanted

• Key milestone dates — Heartbeat, anatomy scan, glucose test, viability, full term

• Comparison of methods — If LMP, ultrasound, and IVF dates differ

It answers the questions every expecting parent asks:

"When is my baby due?"

"How many weeks pregnant am I?"

"When did I conceive?"

"Why does my ultrasound date differ from my LMP date?"

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HOW TO USE THE NUMOVIX PREGNANCY DUE DATE CALCULATOR

Our calculator gives you instant, accurate pregnancy dating in under 30 seconds.

Step 1:

Enter the first day of your last menstrual period (LMP).

Example: March 15, 2026

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Step 2:

Enter your average cycle length (if not 28 days).

Example: 32 days (default is 28)

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Step 3:

Select your dating method.

• LMP only

• Conception date known

• IVF transfer date

• Ultrasound dating

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Step 4:

If known, enter conception date or IVF details.

Example IVF: Embryo transfer on March 28, Day 5 blastocyst

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Step 5:

If using ultrasound, enter scan date and gestational age at scan.

Example: Ultrasound on April 28 showing 8 weeks 3 days

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Step 6:

Click "Calculate Due Date."

You will instantly see:

Example: LMP March 15, 28-day cycle

• Estimated Due Date: December 20, 2026

• Gestational age today (June 6): 12 weeks 0 days

• Fetal age: 10 weeks 0 days

• Trimester: First trimester

• Days remaining: 196 days

• Conception window: March 26 – March 30

• Implantation window: April 2 – April 6

• Next milestone: Nuchal translucency scan (11–14 weeks)

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Example: LMP March 15, 32-day cycle

• Adjusted Due Date: December 24, 2026 (4 days later)

• Gestational age: 11 weeks 3 days (by development)

• Why: Ovulation happened ~4 days later than 28-day cycle assumption

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Example: IVF Day 5 transfer on March 28

• Due Date: December 15, 2026

• Gestational age: 12 weeks 5 days

• Note: IVF dates are often more accurate than LMP because conception is exact

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THE MATH BEHIND DUE DATE CALCULATION

Understanding the formulas helps you trust your date and talk confidently with your provider.

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Naegele's Rule (Standard LMP Method):

EDD = First Day of LMP + 1 year − 3 months + 7 days

Example:

LMP: March 15, 2026

+ 1 year = March 15, 2027

− 3 months = December 15, 2026

+ 7 days = December 22, 2026

Or simply: LMP + 280 days

March 15 + 280 days = December 20, 2026

(Slight variation depending on exact month lengths; calculators use precise day counts.)

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Adjusted Naegele's for Cycle Length:

If your cycle is not 28 days, ovulation timing shifts.

Adjustment = Cycle Length − 28 days

Adjusted EDD = Standard EDD + (Cycle Length − 28)

Example:

Cycle length: 32 days

Difference: 32 − 28 = +4 days

Standard EDD: December 20

Adjusted EDD: December 24

You ovulated 4 days later than the 28-day assumption. Your due date is 4 days later.

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Parikh's Formula (Irregular Cycles):

For highly irregular cycles, a more accurate adjustment:

EDD = LMP + 9 months + (Cycle Length − 21 days)

Example:

LMP: March 15

Cycle length: 35 days

EDD = March 15 + 9 months + (35 − 21) days

EDD = December 15 + 14 days = December 29

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Mittendorf-Williams Rule (First-Time vs Experienced Mothers):

Research shows first-time mothers (nulliparous) average 288 days from LMP.

Mothers with previous births (multiparous) average 283 days.

First-time mother EDD = LMP + 288 days

Experienced mother EDD = LMP + 283 days

Example:

LMP March 15, first baby:

March 15 + 288 days = December 28, 2026 (8 days later than Naegele's)

This rule accounts for longer gestation in primiparous women.

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Conception Date Method:

If you know conception date (e.g., from ovulation tracking or fertility treatment):

EDD = Conception Date + 266 days

Why 266 instead of 280?

Because gestational age counts from LMP (2 weeks before conception). Fetal age is 266 days from conception.

Example:

Conception: March 29

EDD: March 29 + 266 days = December 20, 2026

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IVF Method:

Day 3 Embryo (Cleavage stage):

EDD = Transfer Date + 263 days

(266 days − 3 days embryo age)

Day 5 Embryo (Blastocyst):

EDD = Transfer Date + 261 days

(266 days − 5 days embryo age)

Example:

Day 5 transfer on March 28

March 28 + 261 days = December 14, 2026

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Ultrasound Dating (First Trimester):

Most accurate method in early pregnancy.

Crown-rump length (CRL) correlates tightly with gestational age.

EDD = Ultrasound Date + (40 weeks − Gestational Age at Ultrasound)

Example:

Ultrasound on April 26 shows 8 weeks 0 days

40 weeks − 8 weeks = 32 weeks remaining

April 26 + 32 weeks = December 19, 2026

If ultrasound EDD differs from LMP EDD by more than 7 days, clinicians usually adjust to the ultrasound date.

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Gestational Age vs Fetal Age:

• Gestational Age: Counts from LMP. Used clinically. Pregnancy is 40 weeks gestational.

• Fetal Age: Counts from conception. Used developmentally. Always 2 weeks less.

At 12 weeks gestational = 10 weeks fetal age.

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Complete Real Example:

Priya's Pregnancy Dating Journey:

Scenario 1: LMP Only

• LMP: February 10, 2026

• Cycle length: 28 days (assumed)

• Naegele's EDD: November 17, 2026

Priya tells everyone November 17.

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Scenario 2: Adjusted for Her Actual Cycle

• Priya's real cycle: 31 days

• Adjustment: +3 days

• Adjusted EDD: November 20, 2026

She ovulated 3 days later. The baby is 3 days "younger" developmentally.

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Scenario 3: Early Ultrasound Dating

• 8-week ultrasound on April 7

• CRL measures 8 weeks 2 days

• Ultrasound EDD: November 19, 2026

Close to adjusted LMP. Confirms November 19–20 range.

Her doctor officially records November 20.

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Scenario 4: If She Had IVF

• Day 5 blastocyst transfer: February 21

• IVF EDD: February 21 + 261 days = November 9, 2026

This would be 11 days earlier than her LMP estimate.

Key lesson: Method matters. IVF dates are most reliable. LMP dates are least reliable if cycles are irregular.

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DUE DATE CALCULATION METHODS COMPARED

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TRIMESTER & MILESTONE TIMELINE

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WHY EVERY EXPECTING PARENT NEEDS A DUE DATE CALCULATOR

1. Navigate the Healthcare System

Doctors schedule everything by gestational age.

Your first appointment. Your first ultrasound. Your glucose test. Your Group B strep test.

Without an accurate due date, you get the wrong schedule.

Too early for a heartbeat scan? Anxiety.

Too late for genetic screening? Missed window.

The calculator keeps you on track.

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2. Plan Maternity Leave

Your HR department needs an estimated date.

FMLA qualifies you for 12 weeks. But when do they start?

Your due date determines the timeline.

Calculator gives you the number to file paperwork.

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3. Budget for Baby Expenses

Diapers, nursery furniture, car seat, hospital bag.

When do you need everything ready?

Count back from due date.

36 weeks = pack bag.

32 weeks = install car seat.

20 weeks = start nursery.

Calculator turns "someday" into "Saturday, October 17."

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4. Understand Your Trimester

First trimester: Fatigue, nausea, secrecy.

Second trimester: Energy, bump, anatomy scan.

Third trimester: Discomfort, nesting, countdown.

The calculator tells you exactly where you are.

Not just weeks. The emotional season.

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5. Prepare for the Reality of "Due Date"

The due date is not a delivery appointment.

It is the middle of a window.

37–42 weeks is normal full-term.

Calculator sets the expectation: "Prepare by 37 weeks. Be patient until 42 weeks."

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KEY FACTORS THAT AFFECT DUE DATE ACCURACY

Cycle Length:

28-day cycle = ovulation on day 14.

35-day cycle = ovulation on day 21.

If you use LMP with a 35-day cycle but do not adjust, your due date is 7 days too early.

You look "overdue" at 40 weeks when you are really only 39 weeks.

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Irregular Periods:

Cycles vary month to month? LMP method becomes unreliable.

Ultrasound dating becomes essential.

Parikh's formula or Mittendorf-Williams may help.

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IVF or Assisted Reproduction:

Conception date is known exactly.

IVF due dates are typically more accurate than LMP dates.

Always use transfer date + embryo age.

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Multiple Pregnancies:

Twins often deliver at 36–37 weeks.

Triplets often at 32–34 weeks.

The "due date" still calculates the same, but delivery is usually earlier.

Calculator gives the 40-week mark; your doctor plans for earlier.

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Maternal Health Factors:

Diabetes, hypertension, prior cesarean, placental issues — these may lead to scheduled delivery before 40 weeks.

Due date remains the reference, but actual delivery is medically determined.

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First-Trimester vs Later Ultrasound:

CRL in first trimester (7–13 weeks): ±5 days accuracy.

Second-trimester ultrasound (14–26 weeks): ±10–14 days accuracy.

Third-trimester ultrasound: ±21 days accuracy.

Earlier scans are better for dating.

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COMMON MISTAKES PARENTS MAKE

Mistake 1: Using the Wrong LMP Date

You remember your period started "around March 15."

But was that spotting? Was that the full flow?

Doctors want the first day of full flow.

Being off by 3 days shifts your due date by 3 days.

Being off by a week shifts everything.

Track your periods. Use an app. Write it down.

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Mistake 2: Ignoring Cycle Length

You enter LMP. Calculator assumes 28 days.

But your cycle is 30 days. Your due date is 2 days later.

Those 2 days matter at the end when doctors discuss induction.

Always adjust for your real cycle length.

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Mistake 3: Treating the Due Date as Exact

You tell family: "The baby is coming December 20!"

They call on December 21. "Where is the baby?"

You feel late. Anxious. Pressured.

But 40 weeks is an estimate. Normal range is 37–42 weeks.

Use the calculator to set a due window, not a due deadline.

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Mistake 4: Not Adjusting for IVF

You had IVF. You know exactly when the embryo transferred.

But you still use LMP in the calculator.

Result: Due date is off by days or weeks.

IVF patients should always use the IVF method.

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Mistake 5: Ignoring Ultrasound Dating

Your LMP says December 20.

Your 8-week ultrasound says December 14.

You cling to December 20 because you calculated it yourself.

But ultrasound in first trimester is more accurate than LMP.

Trust the scan. Especially if your cycles are irregular.

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Mistake 6: Not Knowing Gestational vs Fetal Age

You read: "At 10 weeks, the baby has fingers."

You are 12 weeks pregnant by LMP.

You think: "My baby is 12 weeks old."

No. Developmentally, your baby is 10 weeks old.

Gestational age includes the 2 weeks before conception when you were not pregnant.

This matters when reading fetal development guides.

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Mistake 7: Waiting Until 40 Weeks to Prepare

You pack the hospital bag at 39 weeks.

Baby comes at 37 weeks.

You are scrambling.

Calculator shows: Be ready by 36 weeks.

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PRO TIPS FOR EXPECTING PARENTS

Tip 1: Track Your Cycles Before Conception

Use a period tracking app for 3–6 months before trying.

Know your average cycle length.

Know your ovulation window.

This makes your due date calculation accurate from day one.

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Tip 2: Get an Early Ultrasound (7–9 Weeks)

If your LMP is uncertain, cycles are irregular, or you conceived while breastfeeding, schedule an early dating ultrasound.

It is the gold standard for accurate due dating.

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Tip 3: Prepare for a 5-Week Window

Pack bag by 36 weeks.

Install car seat by 35 weeks.

Have nursery ready by 34 weeks.

Full term is 37–42 weeks.

But babies come earlier. And sometimes later.

Plan for the window, not the date.

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Tip 4: Know the Signs of Preterm Labor

Before 37 weeks, call your doctor immediately if you have:

• Regular contractions every 10 minutes

• Water breaking

• Heavy bleeding

• Severe back pain with cramping

The due date is a guide. Labor does not read the calendar.

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Tip 5: Use the Calculator to Count Backwards

Want to know when you conceived?

Enter your due date. Calculator shows conception window.

Helpful for:

• Paternity questions

• Understanding fertility

• Connecting emotionally with the timeline

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Tip 6: Share the Milestone Dates, Not Just the Due Date

Instead of "Due December 20," tell family:

• "Viability at 24 weeks: September 10"

• "Anatomy scan at 20 weeks: August 13"

• "Third trimester starts: September 24"

It spreads the excitement and educates everyone.

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Tip 7: Update the Calculator After Ultrasound

If your ultrasound EDD differs from your LMP EDD by more than 5 days, use the ultrasound date.

Update your apps. Update your calendar.

Accuracy reduces anxiety.

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QUICK SUMMARY

Before you use the calculator, remember these key points:

• Naegele's Rule: LMP + 280 days = standard due date

• Adjust for cycle length if yours is not 28 days — every day matters

• IVF dates are most accurate — use transfer date + embryo age

• First-trimester ultrasound is more accurate than LMP for dating

• Gestational age counts from LMP; fetal age counts from conception (2 weeks less)

• Only 4–5% of babies are born on the exact due date

• Full term is 37–42 weeks — prepare for the window, not the day

• Trimesters divide the 40 weeks into three phases of roughly 13 weeks each

• Milestone dates (heartbeat, anatomy scan, viability) depend on accurate dating

• Irregular cycles make LMP unreliable — prioritize ultrasound dating

• Never treat the due date as a deadline — it is a scientific estimate

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FREQUENTLY ASKED QUESTIONS

Q1: How accurate is the LMP due date method?

Moderately accurate for women with regular 28-day cycles.

Accuracy: ±7 days if cycles are regular and ovulation is predictable.

If cycles are irregular, accuracy drops to ±2–3 weeks.

This is why early ultrasound confirmation is recommended.

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Q2: What if I do not know my LMP?

Use the ultrasound method as soon as possible.

A first-trimester ultrasound can estimate gestational age within ±5 days.

Alternatively, use:

• Date of first positive pregnancy test (roughly 3–4 weeks after LMP)

• Date you first felt pregnancy symptoms

• Conception date if known

But ultrasound is best.

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Q3: Can my due date change?

Yes.

If your early ultrasound suggests a due date more than 7 days different from your LMP date, your provider will usually adjust your official due date.

Later in pregnancy, due dates are rarely changed because fetal growth varies.

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Q4: What if my cycles are irregular?

Do not rely on LMP alone.

Use Parikh's formula or get an early ultrasound.

If your cycles range from 26 to 40 days, ovulation timing is unpredictable.

An 8-week ultrasound gives you a more reliable EDD than any math formula.

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Q5: How is IVF due date calculation different?

IVF eliminates the guesswork of conception timing.

• Day 3 embryo: Transfer date + 263 days

• Day 5 embryo: Transfer date + 261 days

• Day 6 embryo: Transfer date + 260 days

These dates are typically more accurate than LMP-based estimates.

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Q6: Why are only 4% of babies born on their due date?

Because 40 weeks is an average, not a biological timer.

Normal pregnancy length varies:

• First-time mothers: Average 41 weeks 1 day

• Mothers with previous births: Average 40 weeks 3 days

• Range: 37–42 weeks is considered normal full term

The due date is a statistical midpoint, not a delivery appointment.

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Q7: What is the difference between preterm, early term, full term, and post term?

| Category | Gestational Age | Meaning |

| Preterm | Before 37 weeks 0 days | Early delivery, may need NICU |

| Early term | 37 weeks 0 days – 38 weeks 6 days | Full term but early side |

| Full term | 39 weeks 0 days – 40 weeks 6 days | Ideal delivery window |

| Late term | 41 weeks 0 days – 41 weeks 6 days | Monitoring increased |

| Post term | 42 weeks 0 days and beyond | Usually induced |

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RELATED CALCULATORS

Explore our full suite of free health and planning tools:

• Ovulation Calculator

• Implantation Calculator

• Fetal Growth Calculator

• Pregnancy Weight Gain Calculator

• BMI Calculator

• Conception Calculator

• IVF Due Date Calculator

• Trimester Calculator

• Countdown to Baby Calculator

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FINAL THOUGHTS

A due date is just a number.

December 20. November 15. July 3.

But it is the number that organizes everything.

It is the number your doctor writes at the top of your chart.

It is the number your employer puts on your leave form.

It is the number you whisper to family.

It is the number you count down to on your phone.

It is the number that turns abstract joy into a concrete plan.

And yet, the most important thing to remember is this:

That number is an estimate.

Your baby will come when your baby is ready.

Some arrive at 37 weeks, perfect and impatient.

Some arrive at 42 weeks, stubborn and comfortable.

The calculator gives you the map.

But pregnancy is a journey, not a schedule.

Use the calculator to plan your nursery, your leave, your appointments, and your expectations.

But do not let it rule your anxiety.

When the test turned positive, you became a parent.

The due date is just the day the world gets to meet what you already love.

Count the weeks. Celebrate the milestones. Prepare for the window.

And when labor starts — whether on the due date, before it, or after it — you will be ready.

Because you did not just guess. You calculated. You planned. You prepared.

That is how you enter parenthood with confidence.

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DISCLAIMER

This article is for educational and informational purposes only.

Pregnancy dating, due dates, and gestational age calculations are estimates and vary by individual pregnancy, maternal health, and clinical findings.

The examples provided are illustrative and based on standard obstetric dating methods.

Actual due dates and delivery timing depend on:

• Individual cycle length and ovulation timing

• Accuracy of LMP recall

• Ultrasound measurements and dating

• Maternal health conditions

• Fetal development and position

• Medical decisions regarding induction or cesarean delivery

Always confirm your due date and gestational age with a qualified healthcare provider, OB-GYN, or midwife through clinical examination and ultrasound.

Numovix does not provide medical advice, diagnosis, or treatment.

Our calculator results are estimates and should not replace professional prenatal care or medical guidance.

If you have concerns about your pregnancy, due date, or fetal development, consult your healthcare provider immediately.

Pregnancy Due Date Calculator | Calculate EDD, Gestational Age & Trimesters | Numovix

Free pregnancy due date calculator. Calculate your estimated due date (EDD) using LMP, conception date, or IVF transfer date. Track gestational age, trimester milestones, and fetal development week by week. No signup needed.