Pregnancy Due Date Calculator

Calculate your estimated due date (EDD) and track your pregnancy week by week.

First Day of Last Menstrual Period (LMP)

Average Cycle Length 28 days

days

20 days45 days

Estimated Due Date

—

Current Week

—

Trimester

—

Days Remaining

—

Key Milestone Dates

Milestone	Date	Week

👶 What is an Estimated Due Date (EDD)?

The Estimated Due Date (EDD), also called the Expected Date of Delivery (EDD) or Expected Date of Confinement (EDC), is the predicted date on which a pregnancy is expected to reach full term and the baby will be born. It is typically calculated as 280 days (40 weeks) from the first day of the last menstrual period (LMP) using Naegele's rule, named after the German obstetrician Franz Karl Naegele who formulated it in 1812.

Pregnancy is divided into three trimesters. The first trimester (weeks 1–12) begins before conception is even possible — counting starts from the LMP because ovulation and conception dates are often uncertain. During this period, the embryo forms all major organs. The second trimester (weeks 13–26) is typically the most comfortable period, with visible fetal movement and rapid growth. The third trimester (weeks 27–40) sees final weight gain, lung maturation, and preparation for birth.

A pregnancy is considered full-term at 37 weeks and post-term after 42 weeks. The EDD sits at 40 weeks, the midpoint of the full-term window. Statistically, only about 5% of babies are born on their exact EDD — most arrive within two weeks before or two weeks after. The EDD is best understood as a midpoint estimate, not a deadline.

Three calculation methods exist. The LMP method is the most widely used and requires knowing the first day of the last period. For women with irregular cycles, the ultrasound method is more accurate: the sonographer measures the crown-rump length (before 14 weeks) or head circumference and femur length (after 14 weeks) to estimate gestational age. If conception via IVF or timed intercourse is known precisely, the conception date method adds 266 days to the conception date.

Medical disclaimer: This calculator is for informational and planning purposes only. Always consult your obstetrician or midwife for medical advice, pregnancy monitoring, and accurate dating. The EDD provided here is an estimate and should be confirmed by a healthcare professional.

📐 Due Date Formula (Naegele's Rule)

EDD = LMP + 280 days

EDD = Estimated Due Date

LMP = First day of the Last Menstrual Period

280 days = 40 weeks, assuming 28-day cycle (14 days pre-ovulation + 266 days fetal development)

EDD (adjusted) = LMP + 280 − 28 + Cycle Length (in days)

EDD (by conception) = Conception Date + 266 days

EDD (by ultrasound) = Scan Date + (280 − Gestational Age at Scan in days)

Cycle Length Adjustment: for a 35-day cycle, add 7 days to the standard EDD; for a 21-day cycle, subtract 7 days

Gestational Age at Scan = (weeks × 7) + days from ultrasound report

Current Week = ⌊Days since LMP ÷ 7⌋ + 1

Trimester 1: Weeks 1–12 · Trimester 2: Weeks 13–26 · Trimester 3: Weeks 27–40+

📖 How to Use This Calculator

LMP Method (Most Common)

Select "By LMP" tab and enter the first day of your last menstrual period. This is the date your last period started, not when it ended.

Set your average cycle length. Leave at 28 if you have a standard cycle. Adjust up for longer cycles (e.g., 35 days) or down for shorter cycles (e.g., 21 days).

Click Calculate to see your EDD, current week, trimester, and key milestone dates.

Ultrasound Method (Most Accurate)

Select "By Ultrasound" tab. From your ultrasound report, find the date of the scan and the gestational age (in weeks and days) reported by the sonographer.

Enter the scan date and gestational age. The calculator back-calculates your LMP equivalent and determines the EDD from that anchor point.

💡 Example Calculations

Example 1 — Standard 28-Day Cycle

LMP: January 10, 2026 · Cycle: 28 days

EDD = January 10, 2026 + 280 days = October 17, 2026

If today is April 6, 2026: Days since LMP = 86 → Current week = ⌊86 ÷ 7⌋ + 1 = Week 13 (second trimester just started)

Due Date: October 17, 2026 · 195 days remaining · Week 13 of 40 · Second Trimester

Try this example →

Example 2 — Adjusted for Long Cycle

LMP: February 1, 2026 · Cycle: 35 days

Standard EDD (28-day) = February 1 + 280 = November 8, 2026

Cycle adjustment = 35 − 28 = +7 days

Adjusted EDD = November 8 + 7 = November 15, 2026

For a 35-day cycle, the due date is pushed 1 week later to November 15, 2026, reflecting later ovulation.

Try this example →

📋 Pregnancy Week-by-Week Guide

Weeks	Trimester	Key Milestone
1–4	First	Fertilization, implantation, missed period
5–8	First	Heartbeat detectable (week 6), morning sickness begins
9–12	First	First trimester scan; all major organs formed; miscarriage risk drops
13–16	Second	Second trimester begins; visible bump; energy returns
18–20	Second	Anatomy scan (anomaly scan) recommended; gender may be visible
20–22	Second	Quickening — first baby movements felt
24	Second	Viability threshold — fetus can potentially survive outside womb
27–28	Third	Third trimester begins; rapid weight gain; lung development
36	Third	Baby is considered late-preterm; position usually fixed
37	Third	Full-term begins — safe to deliver
40	Third	Estimated Due Date (EDD)
42+	Post-term	Induction usually recommended; increased monitoring

❓ Frequently Asked Questions

How is the pregnancy due date calculated?+

The most common method is Naegele’s rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). This assumes a 28-day cycle with ovulation on day 14. For example, if your LMP is January 1, your EDD is October 8 of the same year. Alternatively, if you know the conception date, add 266 days (38 weeks). If you have an ultrasound, the sonographer measures the fetus and reports a gestational age, which can then be used to back-calculate the EDD.

How accurate is the due date calculation?+

The LMP method is accurate within ±2 weeks for most women with regular 28-day cycles. Ultrasound dating in the first trimester (8–12 weeks) is the most accurate method, typically within ±5 days. After 20 weeks, ultrasound accuracy decreases to ±3 weeks. Only about 5% of babies are born on their exact EDD — most are born within ±2 weeks. The EDD is best understood as the midpoint of a 5-week window (38–42 weeks).

What are the three trimesters of pregnancy?+

The first trimester is weeks 1–12 (months 1–3), covering fertilization, implantation, and major organ formation. The second trimester is weeks 13–26 (months 4–6), when movement is felt and the baby grows rapidly. The third trimester is weeks 27–40 (months 7–9), focused on weight gain and lung development. Full-term is 37–42 weeks; preterm is before 37 weeks; post-term is after 42 weeks.

What is gestational age vs. fetal age?+

Gestational age is counted from the first day of the last menstrual period — this is the standard medical measure. Fetal age (or embryonic age) is counted from conception, which is typically 2 weeks after LMP. So a fetus that is 38 weeks gestational age is actually about 36 weeks old from conception. Doctors and ultrasounds always use gestational age.

What if my cycle is not 28 days?+

If your cycle is longer than 28 days, you likely ovulate later, and your EDD will be later than Naegele’s rule predicts. For example, with a 35-day cycle, add 7 extra days to the LMP-based EDD. If your cycle is shorter (e.g., 21 days), subtract 7 days. The most accurate adjustment is an early ultrasound (8–12 weeks), which directly measures fetal size and gives a more precise EDD regardless of cycle length.

What key milestones happen during pregnancy?+

Key dates include: Week 8 — first heartbeat detectable by ultrasound; Week 12 — first trimester ends, miscarriage risk drops significantly; Week 16–20 — anomaly scan (anatomy scan) is recommended; Week 20 — typically when movement (quickening) is first felt; Week 24 — viability threshold; Week 28 — third trimester begins; Week 37 — full-term begins; Week 40 — EDD; Week 42 — post-term, induction is usually discussed.

What is the conception date and how is it different from LMP?+

The LMP (Last Menstrual Period) date is the first day of your last period. Conception (fertilization) typically occurs about 14 days after LMP, during ovulation. So gestational age (counted from LMP) is always about 2 weeks more than embryonic age (counted from conception). Doctors use gestational age because LMP is known; conception date is often uncertain. If you know your conception date, add 266 days (38 weeks) to get your EDD.

What does the ultrasound due date method mean?+

In an early ultrasound (8–12 weeks), the sonographer measures the fetus — specifically the crown-rump length (CRL) in the first trimester. This measurement is compared against established growth charts to estimate gestational age in weeks and days. The calculator then adds the remaining weeks to 40 to project your EDD. First-trimester ultrasound dating is the most accurate method, often within ±5 days.

What if my due date is different on ultrasound vs. LMP calculation?+

A discrepancy of 1–2 weeks between LMP-based and ultrasound-based EDD is common and usually indicates that your cycle length differs from the assumed 28 days, or that ovulation was earlier or later than day 14. If the discrepancy is more than 2 weeks, your OB will typically reassign the EDD based on the ultrasound, especially in the first trimester. The ultrasound is generally more accurate for irregular cycles.

How do I count pregnancy weeks?+

Pregnancy is counted from the first day of your LMP. Week 1 begins on the LMP date. You are in week 5 from day 29 to day 35. Full term is 37–42 weeks, with 40 weeks being the EDD. Each month is about 4.3 weeks, so 40 weeks ≈ 9.2 months. It is common to say pregnancy lasts ‘9 months,’ but technically it spans parts of 10 calendar months from LMP to EDD.

🔗 Related Calculators

📌 Quick Tips

💡Naegele's rule (LMP method) assumes a 28-day cycle with ovulation on day 14. If your cycle is longer or shorter, the ultrasound EDD is more accurate.

💡Ultrasound dating is most accurate in the first trimester (before 14 weeks). After 20 weeks, gestational age estimates become less precise.

💡A full-term pregnancy lasts 37–42 weeks. Only about 5% of babies arrive on the exact due date - most arrive within 2 weeks either side.