🤰 Due Date Calculator
Calculate estimated pregnancy due date from last menstrual period (LMP) or conception date with gestational age tracking
Your Result:
📅 Your Estimated Due Date
This is an example preview calculation
How to Use This Due Date Calculator
🚨 IMPORTANT PREGNANCY HEALTH WARNING
This calculator provides reference estimates only. Due dates are approximations - only 5% of babies are born on their calculated due date. Always rely on your healthcare provider for accurate pregnancy dating and medical advice. Regular prenatal care is essential for a healthy pregnancy.
How to Use the Due Date Calculator:
- Choose Calculation Method: Select from Last Menstrual Period (most common), Conception Date, IVF Transfer, or Ultrasound dating
- Enter Your Date: Input the relevant date based on your chosen method. For LMP, enter the first day of your last period
- Adjust Cycle Length (Optional): If your cycle isn't 28 days, enter your average cycle length for more accurate results
- IVF Specifics: For IVF pregnancies, select 3-day or 5-day embryo transfer for precise calculations
- Ultrasound Dating: Enter the ultrasound date and the gestational age measured during the scan
- Calculate: Click to see your estimated due date, current gestational age, and pregnancy timeline
- Review Results: View your due date, trimester information, and important pregnancy milestones
Important Notes: This calculator uses Naegele's Rule (LMP + 280 days) for standard calculations. Actual delivery typically occurs between 37-42 weeks. First pregnancies often go past the due date. Multiple pregnancies typically deliver earlier. Always confirm dates with your healthcare provider.
⚠️ MEDICAL DISCLAIMER: This tool is for educational purposes only. It does not provide medical advice. Pregnancy dating should be confirmed by ultrasound and professional medical assessment. For any pregnancy concerns, complications, or medical questions, consult your obstetrician or midwife immediately.
How It Works
Medical Pregnancy Dating Calculations:
Our calculator uses established obstetric formulas to estimate pregnancy due dates based on different dating methods:
- Naegele's Rule (LMP Method): Adds 280 days (40 weeks) to the first day of your last menstrual period. Adjusts for cycle length variations by adding or subtracting days from the standard 14-day ovulation assumption
- Conception Date Calculation: Adds 266 days (38 weeks) from the known conception or ovulation date. More accurate when conception date is certain through ovulation tracking or IVF
- IVF Transfer Dating: For 3-day embryos, adds 263 days from transfer. For 5-day blastocysts, adds 261 days. Accounts for the embryo's developmental age at transfer
- Ultrasound Dating: Calculates backward from the measured gestational age to determine conception, then projects forward 280 days. Most accurate in first trimester when fetal growth is consistent
- Gestational Age Tracking: Continuously calculates current pregnancy week and day, days until due date, and trimester progression based on standard 40-week pregnancy timeline
- Trimester Breakdown: Divides pregnancy into three trimesters: First (weeks 1-12), Second (weeks 13-27), Third (weeks 28-40), with key developmental milestones for each period
The calculator accounts for leap years, varying month lengths, and provides a realistic delivery window (37-42 weeks) since only about 5% of babies arrive exactly on their due date. Early ultrasounds (before 13 weeks) provide the most accurate dating.
When You Might Need This
- • Early Pregnancy Planning - Newly pregnant women calculating their estimated due date from their last menstrual period to plan prenatal care appointments and prepare for baby's arrival
- • IVF Pregnancy Tracking - Couples undergoing fertility treatment using exact embryo transfer dates for precise due date calculation and monitoring pregnancy progression after assisted reproduction
- • Ultrasound Dating Confirmation - Comparing ultrasound-measured gestational age with LMP-based calculations to verify pregnancy dating accuracy and adjust due dates if needed
- • Pregnancy Announcement Timing - Planning when to share pregnancy news with family, friends, and employers based on trimester progression and important milestone dates
- • Maternity Leave Planning - Working mothers calculating exact due dates to coordinate maternity leave start dates, work transitions, and childcare arrangements with employers
- • Multiple Dating Method Comparison - Healthcare providers and patients comparing due dates from different calculation methods (LMP, ultrasound, conception) to determine most accurate estimate
- • Irregular Cycle Adjustments - Women with non-standard menstrual cycles (shorter or longer than 28 days) getting adjusted due date calculations for more accurate pregnancy dating
- • Birth Preparation Scheduling - Planning childbirth classes, hospital tours, baby showers, and nursery preparation based on pregnancy timeline and approaching due date
- • High-Risk Pregnancy Monitoring - Tracking gestational age for scheduled interventions, specialized testing timing, and monitoring pregnancy milestones in complicated pregnancies
- • Partner and Family Planning - Partners and family members understanding pregnancy timeline to plan work schedules, travel arrangements, and support availability around the due date
Frequently Asked Questions
How accurate are due date calculations?
Due date calculations are estimates with natural variation. Only about 5% of babies are born on their exact due date. Most babies arrive within two weeks before or after the calculated date (37-42 weeks). First-trimester ultrasounds are most accurate (±5-7 days), while LMP calculations can vary by ±2 weeks. Factors like cycle irregularity, conception timing uncertainty, and individual variation affect accuracy. Always use professional medical assessment for pregnancy dating. **DISCLAIMER: Consult your healthcare provider for accurate pregnancy dating and monitoring.**
What's the difference between LMP and conception date calculations?
LMP (Last Menstrual Period) calculation adds 280 days from the first day of your last period, assuming ovulation on day 14 of a 28-day cycle. Conception date calculation adds 266 days from actual conception/ovulation, which is more accurate if you know the exact date through ovulation tracking or IVF. LMP is used more commonly because most women know their period date but not their exact ovulation date. The methods typically differ by about 2 weeks since conception usually occurs around day 14 of the cycle.
Should I use ultrasound dating or LMP dating?
Early ultrasound dating (before 13 weeks) is generally more accurate than LMP dating, especially if periods are irregular or LMP is uncertain. Ultrasounds measure fetal size which correlates closely with gestational age in early pregnancy. If ultrasound and LMP dates differ by more than 7 days in first trimester, doctors typically use ultrasound dating. After 20 weeks, ultrasound becomes less reliable for dating as fetal growth varies more. Your healthcare provider will determine the most appropriate dating method for your situation.
How do I calculate my due date with irregular cycles?
For irregular cycles, adjust the standard calculation by accounting for your typical cycle length. If your cycles average 35 days instead of 28, add 7 days to the standard due date. For shorter cycles (e.g., 24 days), subtract 4 days. The calculator adjusts automatically when you enter your average cycle length. However, with very irregular cycles, early ultrasound dating is most reliable. Track several cycles to determine your average, or use ovulation prediction for conception dating. **IMPORTANT: Irregular cycles may indicate underlying conditions requiring medical evaluation.**
Can the due date change during pregnancy?
Yes, due dates can be adjusted based on ultrasound findings, especially if early ultrasounds show significant discrepancy with LMP dating. First trimester adjustments are common and most accurate. After 20 weeks, due dates typically aren't changed unless there's a major discrepancy, as fetal growth becomes more variable. Some providers may adjust dates for consistent growth patterns or specific medical conditions. Multiple ultrasounds help establish growth trends. Remember that the due date is always an estimate, and normal delivery occurs anywhere from 37-42 weeks.