Pregnancy Due Date Calculator
Calculate your estimated due date with medical accuracy using ACOG-approved methods
Due Date Calculator
Quick Tip
Your due date is an estimate – only 4% of babies are born on their exact due date! Most deliveries occur between 37-42 weeks.
Understanding Your Due Date
Calculating your pregnancy due date is one of the first exciting steps in your pregnancy journey. This comprehensive guide explains how due dates are calculated, why they’re important, and what you need to know about pregnancy timelines.
How Pregnancy Due Dates Are Calculated
Pregnancy typically lasts about 280 days (40 weeks) from the first day of your last menstrual period (LMP). This is based on the Naegele’s Rule, developed in the 19th century and still widely used today:
Standard Calculation Formula:
Due Date = First day of LMP + 7 days – 3 months + 1 year
Example: If your LMP was June 1, 2024: June 1 + 7 days = June 8, minus 3 months = March 8, plus 1 year = March 8, 2025
Why Accurate Due Date Calculation Matters
- Prenatal Care Scheduling: Determines timing for important tests and screenings
- Fetal Growth Monitoring: Helps assess if baby is growing appropriately
- Delivery Planning: Guides decisions about induction if pregnancy continues past due date
- Preterm Birth Prevention: Identifies high-risk periods for early delivery
ACOG Guidelines
According to the American College of Obstetricians and Gynecologists (ACOG Committee Opinion No. 700), ultrasound dating in the first trimester is the most accurate method for establishing gestational age, but LMP remains clinically important when menstrual dates are certain.
Three Methods for Calculating Your Due Date
1. Last Menstrual Period (LMP) Method
The most common method assumes a 28-day cycle with ovulation on day 14. If your cycle is longer or shorter, adjustments are made to account for this variation.
2. Conception/IVF Method
If you know your conception date (through fertility tracking or IVF), we calculate forward 266 days (38 weeks) from conception. For IVF pregnancies, we add additional days based on embryo development stage.
3. Ultrasound Method
Early pregnancy ultrasound (before 14 weeks) measures the baby’s size to determine gestational age with 95% accuracy within 5-7 days. Later ultrasounds are less accurate for dating.
Medical Recommendation
If there’s more than a 5-day difference between your LMP-based due date and ultrasound due date before 9 weeks, or more than a 7-day difference between 9-14 weeks, most healthcare providers will use the ultrasound date.
Frequently Asked Questions
Our calculator uses medical-grade algorithms based on ACOG guidelines. With accurate LMP dates, it’s 90% accurate within 2 weeks. First-trimester ultrasound is the most accurate method (95% within 5-7 days).
For irregular cycles, the LMP method is less reliable. Use the ultrasound method if available, or track ovulation through other means. You can adjust your cycle length in the calculator, but ultrasound dating is recommended.
IVF pregnancies are dated from the embryo transfer date plus the embryo’s age. For example, a Day 5 blastocyst transfer: Due date = Transfer date + 266 days + 5 days. Our calculator automatically handles these adjustments.
Only about 4-5% of babies are born on their exact due date. Most births occur between 37-42 weeks. Approximately 80% are born within 2 weeks of their due date (10 days before to 10 days after).
Yes, especially if first-trimester ultrasound measurements differ significantly from LMP dating. Healthcare providers typically only change the due date if ultrasound before 14 weeks shows more than 5-7 days difference from LMP dating.
According to ACOG, term pregnancy is now divided into:
- Early Term: 37 weeks 0 days to 38 weeks 6 days
- Full Term: 39 weeks 0 days to 40 weeks 6 days
- Late Term: 41 weeks 0 days to 41 weeks 6 days
- Postterm: 42 weeks 0 days and beyond
How to Use This Calculator Effectively
Method Selection
Choose the calculation method that matches your situation. Use LMP if you have regular periods, ultrasound if you’ve had early dating scan, or conception/IVF if you know exact dates.
Accurate Dates Matter
The more accurate your input dates, the more reliable your results. Use your menstrual calendar or medical records for precise information.
Medical Consultation
Always discuss your calculated due date with your healthcare provider. They may adjust it based on ultrasound findings or other clinical factors.
Track Progress
Use our calendar feature to mark important milestones: first trimester screening (11-14 weeks), anatomy scan (18-22 weeks), and third-trimester growth scans.
Medical References & Sources
Committee Opinion No. 700: Methods for Estimating the Due Date
WHO recommendations on antenatal care for a positive pregnancy experience
Accuracy of pregnancy dating methods: systematic review
Pregnancy week by week – Due date calculation guidelines
Human gestation: current understanding of the duration of pregnancy
Ultrasound for fetal assessment in early pregnancy
