# Due Date Calculator

Estimate your pregnancy due date and key milestones based on your last period or conception date, free and easy to use today.

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- **Canonical URL:** https://dothecalculation.com/calculators/due-date-calculator
- **Category:** Health and fitness
- **Publisher:** Do The Calculation (https://dothecalculation.com)
- **Cost:** Free, no account or sign-up required
- **Privacy:** Runs entirely in the browser; inputs are never sent to a server
- **Methodology:** https://dothecalculation.com/methodology

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## Pregnancy Due Date Calculator — Calculate Your Baby's Due Date

Use this pregnancy due date calculator to quickly estimate when your baby will arrive. Whether you know the first day of your last menstrual period (LMP), your conception date, or already have a due date from an ultrasound, this tool gives you an instant estimate of your due date, current pregnancy week, and trimester.

- Calculate your due date from your last menstrual period (LMP)
- Calculate your due date from a known conception date
- Work backwards from a due date to find your pregnancy week

## Quick Answer

**What is a due date?** A due date (or estimated date of birth) is the estimated date when your baby is expected to be born.

**The basic calculation:** Due Date = LMP + 280 days (40 weeks)

**Simple example:** LMP: January 1, 2025 → Due Date: January 1 + 280 days = **October 8, 2025**.

**Key facts:**

• Average pregnancy = 40 weeks (280 days) from the first day of your LMP

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

• Most babies arrive between 37 and 42 weeks

**Quick reference:**

• LMP → Due Date: LMP + 280 days

• Conception → Due Date: Conception + 266 days

• 40 weeks = 280 days = full term

## Use the Due Date Calculator

To use this due date calculator:

1. Choose **From LMP**, **From Conception**, or **From Due Date** mode above.

2. Enter the relevant date (and adjust the "as of" date if you want your progress on a day other than today).

3. Review your due date, current pregnancy week, trimester, and days remaining.

**Example input (From LMP mode):** Last Menstrual Period = January 1, 2025, As-of date = August 27, 2025.

**Output:** Estimated Due Date = **October 8, 2025** • Current Pregnancy Week = **Week 34** • Trimester = **Third Trimester** • Days to Due Date = **42 days**.

**Example input (From Conception mode):** Conception Date = January 14, 2025, As-of date = August 27, 2025.

**Output:** Estimated Due Date = **October 7, 2025** • Current Pregnancy Week = **Week 34** • Trimester = **Third Trimester** • Days to Due Date = **41 days**.

Notice the conception-date output lands one day earlier than the LMP example above — that is expected. A conception date of January 14 is only 13 days after an LMP of January 1, not the full 14 days the 266-day rule assumes, so it shifts the whole timeline back a day. Switch to **From Conception** mode above to see this calculated live.

## What Is a Due Date?

A due date (also called the estimated date of birth, or EDD) is the estimated date when your baby is expected to be born. It's calculated from the first day of your last menstrual period (LMP) or from the date of conception.

**Key facts:**

• Pregnancy lasts an average of 40 weeks (280 days) from the first day of your LMP

• This is the medical standard used to calculate due dates worldwide

• The actual birth date varies — most babies arrive between 37 and 42 weeks

**Why it's called an "estimated" date of birth:**

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

• Babies arrive when they're ready — some early, some late

• The due date is a helpful planning guide, not a guarantee

**What is full term?**

• Early term: 37–38 weeks

• Full term: 39–40 weeks

• Late term: 41 weeks

• Post-term: 42 weeks and beyond

## How Does This Calculator Work?

This calculator uses the standard medical formula behind due dates — often called **the 280-day rule**:

**Due Date = LMP + 280 days (40 weeks)**

**Why 280 days?** Pregnancy is counted from the first day of your LMP, but ovulation and conception typically happen around day 14 of the cycle. A baby then grows for approximately 266 days after conception. 266 + 14 = **280 days total**.

**The formula assumes:**

• A regular 28-day menstrual cycle

• Ovulation on day 14

• Conception around day 14

**What if you know the conception date?** Due Date = Conception Date + 266 days. This can be more useful when conception or ovulation was closely tracked. IVF embryo-transfer dating uses transfer-specific offsets, which are handled by the [gestational age calculator](/calculators/gestational-age-calculator).

## How to Calculate Your Baby's Due Date — Step by Step

There are three common ways to estimate a due date by hand. All three should agree with each other when the inputs are truly 14 days apart — small mismatches usually mean the LMP and conception date weren't quite 14 days apart to begin with.

**Method 1: From LMP (most common).** Formula: Due Date = LMP + 280 days.

Step 1 — Identify your LMP: LMP = January 1, 2025. Step 2 — Add 280 days: January 1 + 280 days = **October 8, 2025**. Answer: your baby's due date is **October 8, 2025**.

**Method 2: From conception date.** Formula: Due Date = Conception Date + 266 days.

Step 1 — Identify your conception date: Conception Date = January 15, 2025 (14 days after an LMP of January 1). Step 2 — Add 266 days: January 15 + 266 days = **October 8, 2025**. Answer: your baby's due date is **October 8, 2025**, matching Method 1 exactly, because January 15 is a full 14 days after the January 1 LMP.

**Method 3: Naegele's Rule (quick manual estimate).** Formula: Due Date = (LMP − 3 months + 7 days), adding 1 year back whenever subtracting 3 months moves you into the previous year.

Step 1 — Identify your LMP: LMP = January 1, 2025. Step 2 — Subtract 3 months: January 1 → October 1, **2024**. Step 3 — Add 7 days: October 1 + 7 days = October 8, 2024. Step 4 — Because step 2 crossed into the previous year, add 1 year back: October 8, 2024 + 1 year = **October 8, 2025**. Answer: your baby's due date is **October 8, 2025** — the same answer as Methods 1 and 2, confirming Naegele's Rule is just a hand-arithmetic shortcut for the same 280-day rule.

**A note on Method 3:** many quick explanations of Naegele's Rule leave out step 4 (the "+1 year" correction), which silently produces a due date a full year too early whenever the LMP falls in the first three months of the year. If you calculate by hand and land in the wrong year, that missing step is almost always why — see Common Due Date Mistakes below.

## Due Date from LMP — The 280-Day Rule

The 280-day rule is the most common way to calculate due dates, and it's the method behind this calculator's **From LMP** mode.

**How it works:** Pregnancy is counted from the first day of your LMP, and the average pregnancy lasts 280 days from that date — which includes roughly 2 weeks before conception even happens.

**Why count from before conception?** It's far easier for most people to know their LMP than the exact date of conception, it provides one consistent standard for every pregnancy, and it's the method used by most healthcare providers worldwide.

**Example:** LMP: March 15, 2025 → Due Date: March 15 + 280 days = **December 20, 2025**.

**Important:** this assumes a 28-day cycle. If your cycle runs consistently longer or shorter, your true due date may shift by roughly the same number of days — an early dating ultrasound is the most reliable way to confirm it.

## Due Date from Conception — The 266-Day Rule

If you know the conception date or closely tracked ovulation date, you can use the 266-day rule instead, matched by this calculator's **From Conception** mode.

**How it works:** Conception happens around day 14 of a 28-day cycle, and the baby grows for approximately 266 days after conception. Because 266 + 14 = 280, this method should always agree with the LMP method as long as the conception date really is 14 days after the LMP.

**Example:** Conception Date: March 29, 2025 → Due Date: March 29 + 266 days = **December 20, 2025** (matching an LMP of March 15, 2025 exactly).

**When to use this method:** closely tracked ovulation, a known natural conception date, or an uncertain LMP. For IVF, do not enter the embryo-transfer date as a natural conception date: day-3 and day-5 transfers use different offsets, which the [gestational age calculator](/calculators/gestational-age-calculator) handles separately.

## Pregnancy Week Calculator by Due Date — Working Backwards

Sometimes you already have a due date — from an ultrasound, a clinic, or a previous calculation — but you want to know your current pregnancy week. This calculator's **From Due Date** mode solves exactly that, working the formula in reverse.

**Formula:** LMP = Due Date − 280 days, then Current Week = (Current Date − LMP) ÷ 7, reported as completed weeks.

**Worked example:** Due Date: December 20, 2025. Implied LMP: December 20 − 280 days = March 15, 2025. Current Date: August 27, 2025. Days since LMP: March 15 to August 27 = 165 days. Weeks: 165 ÷ 7 = 23 remainder 4 → **23 weeks, 4 days pregnant**, in the second trimester.

**This is useful when:** you know your due date but not your exact LMP, you want a quick progress check without re-entering your period date, or you're planning maternity leave around a due date your provider already gave you.

## LMP vs. Conception Date vs. Due Date — What's the Difference?

**Last Menstrual Period (LMP):** the first day of your last period. This is the clinical starting point for pregnancy dating, even though you weren't actually pregnant yet on that day.

**Conception date:** the day the egg was fertilized, typically about 14 days after the first day of your LMP in a standard 28-day cycle. This is also called your fetal age's starting point.

**Due date (EDD):** the estimated date of birth, calculated as LMP + 280 days, or equivalently, Conception + 266 days.

**Why the distinction matters:** "gestational age" (what your provider tracks week to week) is counted from LMP, not conception — so at a "6-week" ultrasound, the embryo itself is closer to 4 weeks old developmentally. Mixing these two clocks up is one of the most common sources of due-date confusion; see the [gestational age calculator](/calculators/gestational-age-calculator) for a deeper breakdown of gestational age versus fetal age. Not trying to date a pregnancy, just want your next period predicted? The [Menstrual Cycle Calculator](/calculators/menstrual-cycle-calculator) covers that narrower question on its own.

## How to Calculate a Due Date in Excel

This calculator's audience skews spreadsheet-savvy, so here's how to reproduce every formula above in Excel or Google Sheets.

**From LMP (280-day rule):** with your LMP date in cell B1, use `=B1+280` for the due date.

**From conception (266-day rule):** with your conception date in cell B1, use `=B1+266`.

**Reverse — LMP from a known due date:** with the due date in cell B1, use `=B1-280`.

**Current pregnancy week from LMP:** with LMP in B1 and today's date in B2, use `=INT((B2-B1)/7)` for completed weeks and `=MOD(B2-B1,7)` for the leftover days.

**Naegele's Rule without the year headache:** the textbook version ("subtract 3 months, add 7 days, add 1 year") is easy to get wrong in a spreadsheet. Instead, add 9 months directly — subtracting 3 and adding 12 is the same as adding 9 — with `=EDATE(B1,9)+7`. This lands in the correct year automatically, with no separate year-adjustment step.

**Trimester from LMP-based gestational age (ACOG boundaries):** `=IF(B2-B1<98,"First",IF(B2-B1<196,"Second","Third"))`.

**Days remaining to the due date:** `=B1+280-TODAY()` (formatted as a plain number, not a date).

## Why Due Dates Are Estimates

Your due date is an estimate, not a guarantee.

**The truth about due dates:**

• Only about 5% of babies are born on their exact due date — most arrive before or after

• 37–42 weeks is considered a normal range — full term is a window, not a single day

• An early ultrasound can shift your dates if the baby's measured size suggests a different gestational age

• First-time pregnancies tend to run slightly longer on average

• Every pregnancy is a little different, even for the same person across multiple pregnancies

**Why the range exists:** babies develop at different rates, conception dates are themselves estimates rather than exact, and pregnancy length varies naturally from person to person.

**What you should do:** use the due date as a planning guide, prepare for labor starting around 37 weeks, and trust your care provider's guidance over any calculator, including this one.

## Pregnancy Timeline — What to Expect by Trimester

**First trimester (weeks 1–12):** Weeks 4–5: a positive pregnancy test is typical. Weeks 6–8: first heartbeat often visible on ultrasound. Weeks 8–10: morning sickness may start. Week 12: end of the first trimester.

**Second trimester (weeks 13–27):** Weeks 16–20: anatomy scan window. Weeks 18–22: first movements often felt. Week 24: commonly cited threshold of viability outside the womb. Week 27: end of the second trimester.

**Third trimester (weeks 28–40):** Week 28: third trimester begins. Weeks 32–36: growth scans. Week 37: full term begins. Weeks 38–42: waiting for labor.

**Note on trimester boundaries:** this calculator's actual week/trimester output uses ACOG's precise clinical cutoffs (14w0d and 28w0d, i.e. day 98 and day 196 of gestational age) to stay consistent with the [gestational age calculator](/calculators/gestational-age-calculator). The week ranges above (12/27/40) are the everyday rounded version you'll see most places — the two agree almost exactly, within a few days at each boundary.

**Preparing for labor:** pack a hospital bag from around week 36, put together a birth plan, and learn the signs of labor with your provider ahead of time.

**Tracking weight gain alongside your due date:** once you know how far along you are, the [Pregnancy Weight Gain Calculator](/calculators/pregnancy-weight-gain-calculator) shows the IOM's recommended total and weekly weight-gain range for your pre-pregnancy BMI category, alongside your current week.

## Realistic Multi-Example Scenarios

**Scenario 1 — Standard LMP dating.** LMP: May 5, 2025. Due Date = May 5 + 280 days = **February 9, 2026**. On August 27, 2025 (114 days after LMP), that's **16 weeks, 2 days** — second trimester, with 166 days left to go.

**Scenario 2 — Known ovulation/conception date.** Conception confirmed by ovulation tracking: June 10, 2025. Due Date = June 10 + 266 days = **March 3, 2026**. Implied LMP = May 27, 2025.

**Scenario 3 — Working from a dating-scan due date.** A 9-week ultrasound gives a due date of April 2, 2026. Implied LMP = April 2, 2026 − 280 days = **June 26, 2025**. On August 27, 2025, that's **8 weeks, 6 days** — still first trimester.

**Scenario 4 — Longer-than-average cycle.** With a 34-day cycle, ovulation happens later than day 14, so an LMP-based estimate calculated with the plain 280-day rule (which assumes a 28-day cycle) tends to land a few days too early. If your cycles run long or irregular, use the [gestational age calculator](/calculators/gestational-age-calculator)'s cycle-length adjustment, or rely on an early ultrasound instead.

## Practice Problems

**Problem 1:** LMP is January 15, 2025. What is the estimated due date? Solution: Due Date = January 15 + 280 days = **October 22, 2025**.

**Problem 2:** Conception date is February 1, 2025. What is the due date? Solution: Due Date = February 1 + 266 days = **October 25, 2025**.

**Problem 3:** Due Date is December 1, 2025. What was the LMP? Solution: LMP = December 1 − 280 days = **February 24, 2025**.

**Problem 4:** LMP is April 1, 2025. Today is October 1, 2025. How many weeks pregnant? Solution: Days between April 1 and October 1 = 183 days. Weeks = 183 ÷ 7 = **26 weeks, 1 day**.

**Problem 5:** Due Date is January 15, 2026. Today is August 15, 2025. How many weeks pregnant? Solution: LMP = January 15, 2026 − 280 days = April 10, 2025. Days between April 10 and August 15 = 127 days. Weeks = 127 ÷ 7 = **18 weeks, 1 day**.

**Answers:** 1) October 22, 2025 — 2) October 25, 2025 — 3) February 24, 2025 — 4) 26 weeks, 1 day — 5) 18 weeks, 1 day.

## Common Due Date Mistakes

• **Counting from conception instead of LMP.** Mistake: starting the 280-day count from the conception date. Fix: due dates are counted from LMP — if you only know the conception date, add 266 days instead, not 280.

• **Dropping the "+1 year" step in Naegele's Rule.** Mistake: subtracting 3 months and adding 7 days, then stopping. Fix: whenever that subtraction crosses into the previous year, add 1 year back — otherwise the due date lands exactly 12 months too early.

• **Assuming the due date is exact.** Mistake: expecting the baby to arrive precisely on the due date. Fix: use it as a guide — most babies arrive somewhere in the 37–42 week range.

• **Being off by a day when converting "day 14" to a calendar date.** Mistake: treating "14 days after the LMP" as the LMP's calendar day-of-month plus 14 minus 1. Fix: count 14 full days forward from the LMP date — for an LMP of the 1st, day 14 is the 15th, not the 14th.

• **Not accounting for cycle length.** Mistake: assuming everyone has a 28-day cycle. Fix: irregular or unusually long/short cycles shift ovulation, so an early ultrasound is more reliable than the plain LMP formula.

• **Forgetting to include the current date correctly.** Mistake: off-by-one errors when counting completed weeks. Fix: use completed full weeks (floor division), not rounded weeks — 23 weeks and 4 days is "23 weeks pregnant," not 24.

• **Not checking with a healthcare provider.** Mistake: relying only on a self-calculated date. Fix: always confirm your due date with your doctor or midwife, especially after a dating ultrasound.

• **Waiting until the due date to prepare.** Mistake: assuming there's no rush before the due date itself. Fix: prepare your hospital bag and birth plan starting around week 36–37.

## What This Calculator Can and Cannot Do

**This calculator CAN help with:**

• Estimating your due date from your LMP

• Estimating your due date from a known conception date

• Working backwards from a due date to your current pregnancy week

• Determining your current trimester

• Showing days remaining and percent of pregnancy complete

• Planning around prenatal care and maternity leave dates

**This calculator CANNOT do:**

• Replace professional medical advice or prenatal care

• Confirm pregnancy viability

• Predict your baby's exact delivery date

• Detect pregnancy complications

• Replace ultrasound dating, which is more accurate than any date-based formula once available

• Determine your baby's health status

## Final Summary

A pregnancy due date calculator is a useful first step for any expecting parent tracking their pregnancy journey. Understanding your due date helps you plan prenatal care, monitor your baby's development, and prepare for delivery — while remembering it's an estimate your provider will refine with ultrasound dating.

**Remember the key formulas:**

• Due Date (from LMP): LMP + 280 days

• Due Date (from conception): Conception + 266 days

• LMP (from due date): Due Date − 280 days

• Current week: (Current Date − LMP) ÷ 7, as completed weeks

**Quick reference:**

• First trimester: about weeks 1–13

• Second trimester: about weeks 14–27

• Third trimester: about weeks 28–40

Start now — just enter your dates above in whichever mode matches what you know, and get your due date instantly, completely free.

## Frequently asked questions

### What is a pregnancy due date calculator?

A pregnancy due date calculator estimates when your baby is expected to arrive based on your last menstrual period (LMP), your conception date, or a due date you already have from a scan.

### How do I calculate my baby's due date?

Add 280 days (40 weeks) to the first day of your last menstrual period (LMP). If you know your conception date instead, add 266 days to that.

### What is the estimated date of birth?

The estimated date of birth (EDD) is the same thing as your due date — the estimated date your baby will be born, calculated from your LMP, conception date, or an ultrasound.

### How accurate is a due date calculator?

Due date calculators produce estimates, not guarantees. Only about 5% of babies are born on their exact due date, and most arrive somewhere between 37 and 42 weeks.

### What is a pregnancy week calculator by due date?

It works the due-date formula backwards: it subtracts 280 days from your due date to find your implied LMP, then calculates how many weeks pregnant you are from there. This calculator's "From Due Date" mode does exactly that.

### How do I use a conception date to calculate my due date?

Add 266 days to the conception date. For IVF, many clinics instead use the embryo transfer date with a slightly different offset — see the gestational age calculator for day-3 and day-5 transfer specifics.

### What is full-term pregnancy?

Full term is generally 39–40 weeks. Early term is 37–38 weeks, late term is 41 weeks, and post-term is 42 weeks or beyond. 40 weeks (280 days) is the commonly cited average pregnancy length.

### Why do due dates change after an ultrasound?

An early ultrasound measures the baby directly. If the measured size suggests a different gestational age than the LMP-based estimate, your provider may adjust your due date to match the scan.

### What is the difference between LMP and conception date?

LMP is the first day of your last period. Conception is the date the egg was fertilized, typically about 14 days after the LMP in a 28-day cycle — which is why the LMP method adds 280 days but the conception method only adds 266.

### What if I have an irregular cycle?

The plain LMP method assumes a 28-day cycle, so it's less reliable with irregular cycles. An early ultrasound, or the cycle-length adjustment on the gestational age calculator, is more reliable in that case.

### How do I count pregnancy weeks?

Count completed weeks from your LMP, not rounded weeks — for example, 23 weeks and 4 days is described as "23 weeks pregnant," not 24. Week 1 starts on the first day of your LMP.

### What is Naegele's Rule, and why do some explanations of it give the wrong year?

Naegele's Rule estimates a due date by subtracting 3 months from the LMP and adding 7 days. Many quick explanations stop there, but if that subtraction crosses into the previous year, you also need to add 1 year back — otherwise the estimated due date lands exactly 12 months too early.

### Is this pregnancy due date calculator free?

Yes — completely free, with no registration required.

## Related concepts

- **Last Menstrual Period (LMP)** — The first day of your last period, used as the standard clinical starting point for dating a pregnancy — even though conception hasn't happened yet on that day.
- **Conception Date** — The day the egg was fertilized, typically about 14 days after the LMP in a 28-day cycle. Due date = conception date + 266 days.
- **Naegele's Rule** — A manual shortcut for the 280-day rule: subtract 3 months from the LMP, add 7 days, and add 1 year back whenever that subtraction crosses into the previous year.
- **Gestational Age** — How far along a pregnancy is, measured in completed weeks and days from the LMP — the same clock your provider uses at every prenatal visit.

## Related guides

- [Pregnancy Due Date: How Due Dates Are Calculated and What to Expect](https://dothecalculation.com/blog/health/pregnancy-due-date) — Learn how due dates are estimated from LMP, cycle length, conception, and ultrasound, plus what full term and overdue really mean.
- [Pregnancy Conception: Understanding Fertile Windows and Timing](https://dothecalculation.com/blog/health/pregnancy-conception-windows) — Learn how conception timing works, why luteal phase assumptions matter, and how to estimate fertile days without overtrusting one date.

## Related calculators

- [Conception Calculator](https://dothecalculation.com/calculators/pregnancy-conception-calculator) — Estimate your most likely conception date and fertile window based on your cycle length and last menstrual period today.
- [Gestational Age Calculator](https://dothecalculation.com/calculators/gestational-age-calculator) — Calculate gestational age in weeks and days from your last period, due date, or IVF transfer, with due date and trimester.
- [Pregnancy Calculator](https://dothecalculation.com/calculators/pregnancy-calculator) — Track your pregnancy timeline week by week, including due date, trimester milestones, and baby development stages instantly.
- [Basal Body Temperature Fertility Calculator](https://dothecalculation.com/calculators/basal-body-temperature-calculator) — Check today's waking temperature against your follicular baseline for a post-ovulation thermal shift, and estimate your next period.
- [Menstrual Cycle / Period Calculator](https://dothecalculation.com/calculators/menstrual-cycle-calculator) — Predict your next period, estimated ovulation day, and fertile window from your last period start date and average cycle length.
- [Ovulation Calculator](https://dothecalculation.com/calculators/ovulation-calculator) — Estimate your ovulation date and most fertile days based on your menstrual cycle to help you plan or avoid pregnancy naturally.

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_This calculator provides estimates for educational and planning purposes only. Due dates, gestational weeks, and trimester timelines are approximations based on standard formulas and do not replace personalized prenatal care. Always confirm your due date and pregnancy progress with a licensed OB/GYN or midwife, especially after any dating ultrasound._

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_Source: [Do The Calculation](https://dothecalculation.com/calculators/due-date-calculator). Quote freely with attribution and a link to this page._