Calculator
Pregnancy due date calculator
Naegele's rule adds 280 days to the first day of the last period. That is the due date ACOG describes for a 28 day cycle. If your cycle is not 28 days, this page shifts the date by the difference. Your clinician confirms the date.
How the count works
This calculator uses Naegele's rule: 280 days from the first day of the last menstrual period. ACOG Committee Opinion 700 describes that count for a regular 28 day cycle, with ovulation on day 14. Adding 7 days and subtracting 3 months is the same 280 day count. StatPearls names that count Naegele's rule.
If you enter a cycle other than 28 days, this page moves the date by the same number of days. A 30 day cycle adds 2 days. A 26 day cycle subtracts 2 days. ACOG does not publish that shift. ACOG says the 280 day count assumes 28 days, and an ultrasound confirms or changes the date.
Pregnancy week is counted from that same period. Week 1 starts on the first day. On a 28 day cycle the due date is day 280, which is 40 weeks later. After you calculate, the result shows the pregnancy week you are in today and how much time is left.
ACOG says an ultrasound in the first trimester, through 13 weeks and 6 days, is the most accurate way to confirm gestational age. If an ultrasound before 14 weeks and 0 days differs from the period date by more than 7 days, ACOG says to use the ultrasound date. Before 9 weeks and 0 days, a difference of more than 5 days is a reason to change it. If the pregnancy started with IVF, ACOG assigns the date from the embryo: 261 days from transfer for a day 5 embryo, and 263 days from transfer for a day 3 embryo.
After the birth, start here opens the toddler seasons. How much a newborn should eat covers the first feeds. The toddler sleep schedule picks up at 12 months.
Questions
How is this due date counted?
It adds 280 days to the first day of the last menstrual period. That is the count ACOG describes for a 28 day cycle. A longer or shorter cycle moves the date by the same number of days.
What if my cycle is not 28 days?
Enter the usual cycle length. The date shifts by the difference from 28. A 30 day cycle adds 2 days. A 26 day cycle subtracts 2 days.
Will my clinician use this date?
Maybe as a starting point. An exam or ultrasound can change it. The date in the chart is the one to plan around.
How do I calculate a baby's due date?
Add 280 days to the first day of the last period. That is Naegele's rule, and it is the count ACOG describes for a 28 day cycle. This page does that, then shifts the date if you enter a different cycle length.
Is this a pregnancy due date predictor?
It predicts a date from the last period. ACOG says a first trimester ultrasound is the most accurate way to confirm or change that date. If the ultrasound before 14 weeks and 0 days differs by more than 7 days, use the ultrasound date.
Can this show pregnancy week by week?
Yes. After you calculate, the result shows the pregnancy week counted from the last period. On a 28 day cycle the due date is 40 weeks, which is 280 days.
What is a pregnancy tracker due date?
It is this same date: 280 days from the last period on a 28 day cycle, then adjusted here if your cycle is longer or shorter. The date in your clinician's chart is the one to track.
Source
- American College of Obstetricians and Gynecologists. Committee Opinion 700: Methods for estimating the due date. acog.org
- StatPearls. Estimated date of delivery. Naegele's rule subtracts 3 months and adds 7 days to the last menstrual period, a 280 day count. ncbi.nlm.nih.gov/books/NBK536986
Related: Ovulation calculator, Start here, how much a newborn should eat, toddler sleep schedule by age.