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
Monday, October 7, 2024
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 Naegele-style method adds 280 days (40 weeks) to the first day of your last menstrual period. It assumes a roughly 28-day cycle with ovulation near day 14, so irregular cycles may need ultrasound dating. Enter the LMP date carefully. This output is an educational estimate; your prenatal provider sets the official clinical due date.
How is due date calculated from conception?
From a known conception date, about 266 days (38 weeks) are added because conception typically occurs roughly two weeks after LMP in a textbook cycle. Conception date is often estimated unless confirmed by IVF transfer dating or early ultrasound. Use conception mode only when you have a reliable date; otherwise LMP or clinical dating is safer.
How accurate is a due date estimate?
Only about 5% of babies arrive on the exact due date. Most are born within about two weeks before or after. Early ultrasound dating can refine estimates, especially with uncertain LMP or irregular cycles. Treat the calendar date as a planning center point, not a guaranteed delivery day, and follow your clinician’s official dating.
What are the three trimesters?
First trimester commonly runs through week 12, second through week 26, and third from week 27 until delivery, though some sources use slightly different cutoffs. This calculator maps gestational age to those educational bands. Prenatal visit schedules and screening tests follow your provider’s protocol, which may not match every website’s trimester labels exactly.
Should I rely on this instead of my doctor?
No. This is an educational estimate for orientation only. Your prenatal care provider uses menstrual history, exam findings, and ultrasound to establish official dating and monitor pregnancy health. Contact a clinician for confirmation of pregnancy, bleeding, pain, or other symptoms—do not use an online due date tool in place of medical care.