Pregnancy Due Date Calculator - Estimated Delivery Date & Gestational Age
Estimate your baby's due date from the first day of your last menstrual period or your conception date. See gestational age, current trimester, and days until due date.
Pregnancy Dates
LMP + 280 days or conception + 266 days.
Due Date Estimate
Estimated Due Date
Tuesday, February 23, 2027
Methodology and limitations
Last reviewed:
Methodology
Applies Naegele's rule: due date = first day of last menstrual period plus 280 days (40 weeks), or conception date plus 266 days. Reports gestational age, trimester, and days remaining.
Limitations
Only about 5% of babies arrive on the estimated due date. Ultrasound dating in the first trimester is more accurate than LMP alone for irregular cycles.
Official sources
How Pregnancy Due Dates Are Calculated
Estimate your baby's due date from the first day of your last menstrual period or your conception date. See gestational age, current trimester, and days until due date.
Method used
The calculator applies Naegele's rule: add 280 days (40 weeks) to the first day of the last menstrual period, or 266 days (38 weeks) from conception date. It then reports gestational age, trimester, and days until due date.
Due date (LMP) = LMP + 280 days; gestational weeks = days since LMP ÷ 7
Practical example
With a last period starting January 1, 2026, the estimated due date is October 8, 2026, placing the pregnancy at about 12 weeks in late March.
- Method: last menstrual period or conception date
- Start date in YYYY-MM-DD format
The result shows due date, gestational weeks and days, current trimester, and days remaining.
Assumptions
- LMP method assumes a 28-day cycle with ovulation around day 14.
- Conception date method uses 266 days from conception.
- Ultrasound dating may override calendar estimates.
What this includes
- Estimated due date, gestational age, trimester label, and countdown to due date.
What this excludes
- First-trimester ultrasound dating, IVF transfer-date calculations, high-risk pregnancy monitoring, and labor induction scheduling.
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Frequently Asked Questions
How is a due date calculated from LMP?
The standard method adds 280 days (40 weeks) to the first day of your last menstrual period. This assumes a 28-day cycle with ovulation around day 14.
How is due date calculated from conception?
From known conception, 266 days (38 weeks) are added. Conception date is often estimated unless confirmed by IVF or early ultrasound dating.
How accurate is a due date estimate?
Only about 5% of babies arrive on the exact due date. Most are born within two weeks before or after. Early ultrasound dating can refine the estimate.
What are the three trimesters?
First trimester runs through week 12, second through week 26, and third from week 27 until delivery. Trimester boundaries can vary slightly by source.
Should I rely on this instead of my doctor?
No. This is an educational estimate. Your prenatal care provider uses clinical history, exams, and ultrasound to establish official dating.