Due Date Calculator | OmniCalculator

  • Adam
  • November 1, 2025

Free pregnancy due date calculator. Calculate estimated due date using LMP, ultrasound, conception date, or IVF transfer. Includes Naegele’s rule and pregnancy timeline.

🤰 📅 👶

Due Date Calculator

Calculate your estimated due date based on your last period, ultrasound, conception date, or IVF transfer. Get your pregnancy timeline and development milestones.

📋 Quick Navigation

🤰 Calculate your estimated due date! 📅
First day of your last menstruation
21-35 days (average 28)
Date of your ultrasound scan
weeks (typically 8-12 for dating)
0-6 days
Date of conception or ovulation
Date embryo was transferred
age of embryo
Estimated Due Date
TBD
approximately 40 weeks of pregnancy

Due Date

—
delivery date

Weeks Pregnant

40
weeks

Days Pregnant

280
days

Current Week

—
today's week

📊 Pregnancy Timeline

Event Estimated Date Weeks Notes
Last Period (LMP) — Week 0 Official start of pregnancy
Conception — Week 2 Egg fertilized by sperm
Implantation — Week 3-4 Embryo implants in uterus
Positive Test — Week 4 hCG detectable
First Ultrasound — Week 8-12 Dating scan
Second Trimester — Week 13 Risk of miscarriage drops
Anatomy Scan — Week 18-22 Detailed ultrasound
Viability — Week 24 Baby can survive if born
Third Trimester — Week 27 Final trimester begins
Early Term — Week 37 Labor can begin
Full Term — Week 39 Complete pregnancy
Due Date — Week 40 Estimated delivery

🤰 Pregnancy Timeline & Development

First Trimester (Weeks 1-12)

Weeks 1-4: Ovulation, fertilization, implantation. Embryonic development begins. Weeks 5-8: Heart begins beating, neural tube forms, limbs develop. Weeks 9-12: All major organs forming, fetal movement may begin, risk of miscarriage decreases significantly.

Second Trimester (Weeks 13-26)

Weeks 13-16: Baby can hear, genetic testing available, visible baby bump. Weeks 17-20: Detailed anatomy ultrasound performed, sex often determined, fetal movements become stronger. Weeks 21-26: Baby gains weight rapidly, brain development continues, baby's eyes open.

Third Trimester (Weeks 27-40+)

Weeks 27-30: Baby gains weight, brain development accelerates. Weeks 31-34: Baby positions head-down, birth practitioner checks fetal position. Weeks 35-37: Baby drops into pelvis (engagement), final weight gain begins. Weeks 38-40+: Full-term pregnancy, labor can begin anytime.

💡 Important: Only about 5% of babies arrive on their exact due date. Most arrive within 2 weeks. Healthcare providers typically induce labor at 42 weeks if baby hasn't arrived.

📐 Due Date Calculation Methods

Last Menstrual Period (LMP) Method

The most common method. Pregnancy is counted as 280 days (40 weeks) from the first day of LMP, even though conception typically occurs 2 weeks later. Assumes a regular 28-day cycle with ovulation on day 14. Accuracy: ±2 weeks.

Ultrasound Method

Most accurate, especially in first trimester. Based on fetal measurements and developmental stage. First trimester ultrasound (before 12 weeks): ±3-5 days accuracy. Second trimester (12-20 weeks): ±1-2 weeks. Third trimester: ±2-3 weeks.

Conception Date Method

If you know exact conception date, pregnancy lasts 266 days (38 weeks) from conception. More accurate for irregular cycles or assisted reproduction. Add 266 days to conception date for due date.

IVF Transfer Method

Based on embryo age at transfer. Day 3 embryo + 263 days = due date. Day 5 embryo + 261 days = due date. Day 6 embryo + 260 days = due date. Accounts for when embryo development actually began.

📌 Note: All methods provide estimates. Ultrasound dating, especially early in pregnancy, is most accurate. Your healthcare provider will adjust due date based on ultrasound findings if they differ from LMP calculation.

🧮 Calculation Formulas

Naegele's Rule (LMP Method)

Due Date Calculation:
1. Add 7 days to first day of LMP
2. Subtract 3 months
3. Add 1 year (if month after subtraction is invalid)

Example: LMP = November 2, 2025
Nov 2 + 7 days = Nov 9
Nov − 3 months = Aug
Due Date = August 9, 2026

Alternative: LMP + 280 days
Nov 2 + 280 days = August 9, 2026

Cycle-Adjusted Method

For cycles longer or shorter than 28 days:
Due Date = LMP + 280 + (Cycle Length − 28)

Example: LMP Nov 2, 35-day cycle
Due Date = Nov 2 + 280 + 7 = August 16, 2026

Conception Date Method

Due Date = Conception Date + 266 days
Or: Due Date = Conception Date + 38 weeks

Example: Conception Nov 16, 2025
Due Date = Nov 16 + 266 = August 9, 2026

Ultrasound-Based Calculation

Due Date = Ultrasound Date + (40 − Gestational Age in Weeks) × 7 days

Example: US Dec 10, shows 12 weeks
Due Date = Dec 10 + (40 − 12) × 7
Due Date = Dec 10 + 196 days = August 23, 2026

IVF Transfer Calculation

For Day 3 embryo:
Due Date = Transfer Date + 263 days

For Day 5 embryo:
Due Date = Transfer Date + 261 days

Example: Day 5 transfer Nov 16, 2025
Due Date = Nov 16 + 261 = August 4, 2026

❓ Frequently Asked Questions

Why is my due date different from my calculation? +
Ultrasound dating is more accurate than LMP calculation. If ultrasound shows different dating, that's adjusted due date. It's based on fetal measurements which are more precise than cycle length. Due dates commonly shift by a few days after first ultrasound.
When will I go into labor? +
Due date is estimated for week 40, but 90% of babies arrive between week 38-42 (2 weeks before or after due date). Only 5% arrive on exact due date. Signs of labor include contractions, water breaking, and bloody show. Contact your doctor when labor seems to begin.
What is the difference between gestational age and fetal age? +
Gestational age is measured from LMP (even though baby conceived 2 weeks later), so at "8 weeks" gestational age, baby is actually only 6 weeks old developmentally. Fetal age is 2 weeks behind gestational age. Doctors use gestational age for medical tracking and development.
What if I have irregular periods? With irregular cycles, LMP dating is less reliable. An early ultrasound (before 12 weeks) is best for accurate dating. If you know your conception date, use that. For IVF pregnancies, dating from transfer is most accurate. Your doctor can help determine correct due date.
When is early term vs full term? +
Early term: Weeks 37-38 (labor management can begin). Full term: Weeks 39-40+ (optimal for delivery). Births before 37 weeks are preterm. Births after 42 weeks are postterm. Most doctors recommend induction by 42 weeks to reduce complications.
How do I know my baby is growing normally? +
Regular prenatal visits with ultrasounds track growth. First ultrasound establishes accurate due date. Anatomy scan at 18-22 weeks checks major structures. Growth scans later in pregnancy ensure baby is growing appropriately. Your doctor monitors fetal development throughout pregnancy.
What is induction of labor? +
Induced labor is when doctors use medication (pitocin) or methods (breaking amniotic sac) to start labor if it hasn't begun naturally. Common reasons: past due date (42 weeks), maternal health issues, or fetal concerns. Induction success rates are highest in people already in labor-like state.

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