Pregnancy Due Date Calculator
Calculate Estimated Date of Delivery (EDD), gestational age, and trimester boundaries using clinical Naegele's rule.
About Naegele's Rule for Due Dates
Naegele's rule estimates obstetric delivery date assuming a standard human gestation period of 280 days (40 weeks) counted from the first day of the last menstrual period.
Formula
EDD = LMP + 1 Year - 3 Months + 7 Days + (Cycle Length - 28 Days)
Frequently Asked Questions
What percentage of babies arrive exactly on their due date?
Approximately 4% to 5% of births occur on the precise calculated due date; most arrive within two weeks before or after.
How does cycle length affect due date?
Longer cycles delay estimated ovulation, shifting the due date later by the corresponding number of days past 28.
When does the second trimester begin?
The first trimester spans weeks 1 through 12, the second spans weeks 13 through 27, and the third runs from week 28 to delivery.
Is an early ultrasound more accurate than LMP?
Yes. First-trimester crown-rump length (CRL) ultrasound measurements have a margin of error of only +/- 3 to 5 days.
Calculate in three steps
- 1Enter your valuesUse the fields above and check the units shown beside each input.
- 2Run the calculationSelect Calculate to refresh the result with your latest values.
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