Pregnancy Due Date Calculator
Free pregnancy due date calculator. Enter the first day of your last menstrual period and your cycle length to estimate your due date, gestational age, and trimester.
This pregnancy due date calculator uses Naegele's rule: it adds 280 days (40 weeks) to the first day of your last menstrual period to estimate your due date. If your cycle is longer or shorter than the typical 28 days, the tool adjusts the estimate accordingly, since ovulation timing shifts with cycle length. It also shows your current gestational age in weeks and days and which trimester you are in.
Only about one in twenty babies arrives on the exact estimated date, and a normal full-term birth can happen any time between 37 and 42 weeks. These results are estimates for general information only and are not medical advice — an ultrasound and your healthcare provider give the most accurate dating.
Frequently asked questions
How is the due date calculated?
It adds 280 days to the first day of your last menstrual period (Naegele's rule), then adjusts for cycle lengths other than 28 days.
What if my cycle is not 28 days?
Enter your actual cycle length. The calculator shifts the due date by the difference between your cycle and 28 days to account for later or earlier ovulation.
How accurate is an estimated due date?
It is only an estimate. Most babies are born within two weeks either side of the date, and an early ultrasound usually gives more accurate dating than the last period.
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