Due Date Calculator
Calculate your baby's expected due date based on last menstrual period or conception date.
About Due Date Calculator
Calculate your due date and current trimester based on either your last menstrual period (LMP) or conception date. Full-term pregnancy is approximately 40 weeks from LMP or 38 weeks from conception.
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How to Use This Calculator
- Choose your calculation method: Last Menstrual Period (LMP) or Conception Date
- If using LMP: select the first day of your last period
- If using conception date: select the date you conceived or ovulated
- Click 'Calculate Due Date' to see your results
- Review your estimated due date
- Check your current week of pregnancy
- See which trimester you're currently in
- Note your estimated conception date
- Review the trimester breakdown for pregnancy milestones
Formula
From LMP: Due Date = LMP + 280 days (40 weeks); From Conception: Due Date = Conception Date + 266 days (38 weeks); Gestational Age = (Today - LMP) / 7 weeks; Conception Date ≈ LMP + 14 days
Frequently Asked Questions
What's the difference between LMP and conception dating?▼
LMP (Last Menstrual Period) dating adds 280 days from the first day of your last period. Conception dating adds 266 days from the actual conception date. LMP is used medically because it's easier to remember, even though conception typically occurs about 2 weeks after LMP.
Which method is more accurate?▼
If you know your exact conception date (from IVF, IUI, or confirmed ovulation), that method is more accurate. For most pregnancies, LMP dating is standard. Early ultrasound (8-13 weeks) is the most accurate method and may adjust your due date.
What is considered full-term pregnancy?▼
Full-term is now categorized as: Early term (37-38 weeks), Full term (39-40 weeks), Late term (41 weeks), Post term (42+ weeks). The ideal delivery time is 39-40 weeks when the baby is fully developed and lowest risk of complications.
How do ultrasounds determine due dates?▼
Early ultrasounds (8-13 weeks) measure the crown-rump length (CRL) or biparietal diameter. These measurements are compared to standardized growth charts to estimate gestational age within ±5-7 days, making them more accurate than LMP dating alone.