Pregnancy Due Date Calculator
Estimate a due date from the first day of the last menstrual period. Your work stays on this device whenever possible.
How to use Pregnancy Due Date Calculator
- Open Calculation Method and choose Last Menstrual Period (LMP), Conception Day, IVF 3-Day Embryo Transfer, IVF 5-Day Blastocyst Transfer or Ultrasound Dating.
- Set the Reference field to the calendar day that matches your method, such as the first day of the last period or the embryo transfer.
- For LMP, adjust Average Cycle Length (days) if it is not 28; the estimated delivery day shifts by the difference.
- For ultrasound dating, fill Ultrasound Gestation Weeks and Days from the scan report.
- Press "Estimate" and read the expected delivery day, gestational age, trimester and milestone schedule.
Worked example
Choose IVF 5-Day Blastocyst Transfer and set the reference field to 2026-05-04. The calculator adds 261 days, giving an estimated arrival of Wednesday, Jan 20, 2027. It also works back to an estimated LMP 19 days before the transfer, and derives the gestational age, trimester and milestone schedule from that.
When to use this tool
- Getting a first-pass delivery estimate from the first day of the last period.
- Converting an IVF transfer day into an expected arrival.
- Entering a scan's gestational age to see the timeline it implies.
Important limitations
Most babies arrive within the weeks surrounding their estimated due date rather than on the exact date itself. ACOG and NICHD define early term as 37w0d to 38w6d, full term as 39w0d to 40w6d, late term as 41w0d to 41w6d, and post-term as 42w0d and beyond. Ultrasound dating by a licensed clinician remains the clinical reference.
Frequently asked questions
How does each method reach the expected delivery day?
LMP adds 280 days plus any cycle adjustment (Naegele's rule, endorsed by the American College of Obstetricians and Gynecologists: acog.org/clinical/clinical-guidance/committee-opinion/articles/2017/05/methods-for-estimating-the-due-date), conception adds 266, a 3-day transfer 263 and a 5-day blastocyst transfer 261. Ultrasound uses 280 minus the days of gestation found at the scan. Results are an estimate, not medical advice.
Does a longer cycle change the estimate?
Only for the LMP method. A 30-day cycle adds two days to the 280, assuming later ovulation. The cycle field has no effect with conception, transfer or ultrasound methods.
What is the counter of days remaining based on?
It compares the estimated delivery day with today in your browser, so the countdown changes daily. If that day has passed, the calculator reports days past term.
Is the milestone list medical guidance?
No. It gives calendar estimates from the estimated LMP for the end of the first trimester (13w0d), week 24, and the ACOG / NICHD term intervals (nichd.nih.gov/ncmhep/initiatives/know-your-terms/moms): early term (37w0d–38w6d, +259 days), full term (39w0d–40w6d, +273 days), estimated due date (40w0d, +280 days), late term (41w0d–41w6d, +287 days), and post-term (42w0d+, +294 days). All dates are an estimate, not medical advice; clinical decisions should follow a midwife or doctor's scan-based dating.
Why is my result different from my clinic's?
Clinics may re-date from an early ultrasound if it disagrees with the LMP result by more than a few days. The calculator cannot see your scans, so use the ultrasound method with those figures.