Can I use a due date calculator with irregular periods?

Yes. Use the cycle length field in the pregnancy due date calculator to enter your actual cycle length (21–45 days). The calculator adjusts the estimated due date accordingly. For very irregular cycles, an early ultrasound remains the most reliable dating method.

Pregnancy Due Date Calculator 2026 – Drivenly

Pregnancy Due Date Calculator

Pregnancy Due Date
Calculator

Use this free pregnancy due date calculator to estimate when your baby will arrive. Enter your last menstrual period or conception date — we'll calculate your EDD, trimester, and how far along you are in seconds.

Updated June 23, 2026

Written by Sarah Mitchell, RN

Reviewed by Dr. Amara Osei, OB-GYN

6 sources cited ↓

Medical disclaimer: This pregnancy due date calculator is for general educational purposes only. Due dates are estimates — only ~4% of babies arrive on the exact date. Always consult your doctor or midwife for clinical guidance.

Pregnancy Due Date Calculator

Choose a calculation method, enter your date, and get your estimate instantly.

Your estimated due date

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Currently at

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Trimester

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Weeks left

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Days to go

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Pregnancy progress 0%

Week 1Week 13Week 27Week 40

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Baby is about the size of — this week

This is a general estimate based on standard 40-week / 266-day calculations. Only a healthcare provider can confirm your pregnancy timeline through clinical assessment.

Now that you have your due date — what's next?

See your trimester breakdown ↓ Read our pregnancy FAQs ↓ When to seek urgent care ↓

About due dates

What is a pregnancy due date?

A pregnancy due date — formally called the Estimated Due Date (EDD) — is when a healthcare provider expects a baby to be born. Our free pregnancy due date calculator estimates this as approximately 40 weeks from the first day of the last menstrual period (LMP), assuming a 28-day cycle.

According to ACOG Committee Opinion No. 700 [1], only about 4% of babies are born on their exact due date — most arrive within a two-week window either side of it. That's why this tool gives you an estimate to plan around, not a guarantee to count on.

Weeks to full term

Standard LMP-to-EDD duration

8–13

Weeks for dating ultrasound

The most accurate window

Three ways to estimate

How is a pregnancy due date calculated?

Each method uses a different anchor point. Ultrasound is the most precise — the other two are useful starting estimates your pregnancy due date calculator can use.

Naegele's Rule (LMP)

The most widely used formula, described by obstetrician Franz Karl Naegele [2]. Add 280 days to the first day of your last period.

LMP + 280 days

e.g. LMP Sep 1, 2025 → EDD Jun 8, 2026

Conception date

If you know your exact conception or ovulation date, add 266 days. Particularly useful for tracked ovulation cycles.

Conception + 266 days

Best for IVF, fertility tracking

Gold standard

Ultrasound dating

A first-trimester scan (8–13 weeks) measures fetal crown-rump length and is the most accurate method [4].

CRL measurement

ACOG: use this if it differs from LMP by 5–7+ days [1]

Week by week

Pregnancy trimesters and weeks explained

Forty weeks, three stages. Here's what's happening — and what care to expect — at each point along the way. Use the pregnancy due date calculator above to see exactly where you fall.

Use the calculator above to see exactly where you are on this timeline.

You

Week 1 Week 13 Week 27 Week 40

Weeks 1–12 · First trimester

First Trimester: Weeks 1–12

Major organs form; heartbeat detectable around week 6.

Care: dating ultrasound, blood tests

Weeks 13–26 · Second trimester

Second Trimester: Weeks 13–26

Movement typically felt around weeks 18–22; anatomy scan performed.

Care: anatomy scan, glucose screening

Week 27–40+ · Third trimester

Third Trimester: Weeks 27–40

Rapid growth as baby positions for birth.

Care: weekly check-ups, GBS test (~36 wks)

Early term

37w0d – 38w6d

Full term

39w0d – 40w6d

Late term

41w0d – 41w6d

Post-term

42w0d +

What affects accuracy

Factors that can shift your pregnancy due date

An EDD is a statistical estimate. These six factors are the most common reasons your actual delivery date might land earlier, later, or just be harder to pin down in the first place.

Cycle length

If your cycle isn't 28 days, adjust the cycle length field above or ask for an early ultrasound.

PCOS

Can cause unpredictable ovulation, making LMP-based dating less reliable.

IVF / Assisted

The exact fertilization date is known — use the conception date method for greater precision.

Multiples

Twins are often born around 36–37 weeks, earlier than a singleton pregnancy.

Prior preterm birth

One of the strongest predictors of early delivery in a subsequent pregnancy [3].

Health conditions

Gestational diabetes or hypertension can influence timing and delivery planning.

When to seek urgent care during pregnancy

Contact your doctor or call emergency services immediately if you notice any of these signs.

Heavy vaginal bleeding

Severe abdominal pain

Sudden facial or hand swelling

Vision changes or severe headache after 20 weeks

Decreased fetal movement after 28 weeks

Regular contractions before 37 weeks

In the UK, call NHS 111. In the US, contact your OB-GYN's after-hours line or go to the nearest emergency department.

Most pregnancies never experience any of these signs — this list exists so you know what to watch for, not what to expect.

Common questions

Frequently Asked Questions About Pregnancy Due Dates

?How is a pregnancy due date calculated?

A pregnancy due date is calculated using Naegele's Rule: add 280 days to the first day of your last menstrual period. If you know your conception date, add 266 days instead. A first-trimester ultrasound is the most accurate method.

?How accurate is a due date calculator?

A pregnancy due date calculator gives an estimate, not a guarantee. Only about 4% of babies arrive on their exact calculated date. First-trimester ultrasound (8–13 weeks) is the gold standard for accuracy.

?What trimester am I in?

First trimester: weeks 1–12. Second trimester: weeks 13–26. Third trimester: week 27 through birth. Enter your LMP into the pregnancy due date calculator above to see your trimester instantly.

?Can I use this with irregular periods?

Yes — use the cycle length field in the calculator to enter your actual cycle (21–45 days). For very irregular cycles, an early ultrasound remains the gold standard for accurate pregnancy due date estimation.

?How is an IVF due date calculated?

From the egg retrieval date, add 266 days. For a 3-day transfer, add 263 days; for a 5-day blastocyst transfer, add 261 days. Use the conception date option in the pregnancy due date calculator above.

?Does a prior preterm birth affect this?

A prior preterm birth does not change how your pregnancy due date is calculated, but it is one of the strongest predictors of early delivery in a later pregnancy. Your provider will likely monitor you more closely.

About the authors

Sarah Mitchell, RN

Author · Registered Nurse

Sarah is a registered nurse with over eight years of experience in obstetric and maternity care. She has supported hundreds of patients through prenatal appointments, labour ward assessments, and postpartum recovery. Sarah writes and reviews health content to make clinical knowledge accessible to expecting parents.

LinkedIn profile NMC register

Content reviewed for medical accuracy

Dr. Amara Osei, OB-GYN

Medical Reviewer · Obstetrician-Gynecologist

Dr. Osei is a board-certified obstetrician-gynecologist with specialist training in maternal-fetal medicine. She reviews all clinical content on Drivenly to ensure accuracy against current ACOG guidelines and evidence-based obstetric practice.

LinkedIn profile ABOG board certification

Medical review · Last reviewed June 23, 2026

Medical sources & references

1. American College of Obstetricians and Gynecologists (ACOG). Methods for Estimating the Due Date. Committee Opinion No. 700. acog.org
2. Naegele FC. Erfahrungen und Abhandlungen aus dem Gebiete der Krankheiten des weiblichen Geschlechtes. Mannheim, 1812.
3. World Health Organization (WHO). Preterm birth fact sheet. who.int
4. Hadlock FP et al. Estimation of fetal age: computer-assisted analysis of multiple fetal growth parameters. Radiology. 1984.
5. NHS UK. Your antenatal care. nhs.uk
6. Mongelli M, Wilcox M, Gardosi J. Estimating the date of confinement: ultrasonographic biometry versus certain menstrual dates. Am J Obstet Gynecol. 1996.

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