Pregnancy Due Date Calculator
Estimate your due date and key pregnancy milestones. Enter the first day of your last menstrual period (LMP) and your average cycle length — the calculator applies Naegele's rule with a cycle adjustment.
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Result
Please select the first day of your last period.
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Save ⟶How to use the Pregnancy Due Date Calculator
- 1Enter first day of last menstrual period in the form on the left.
- 2Fill in the remaining fields — the result updates automatically as you type.
- 3Review the highlighted result and the supporting breakdown on the right.
- 4Use Copy, Share or Print to save or send your result.
How due dates are calculated
Naegele's rule adds 280 days (40 weeks) to the first day of your last menstrual period, assuming a 28-day cycle with ovulation on day 14. For longer or shorter cycles, the date shifts by the difference — this calculator applies that adjustment automatically.
First-trimester ultrasound dating is more accurate than LMP dating and providers will usually adopt the ultrasound date if it differs by more than about a week.
Frequently Asked Questions
▸How accurate is a due date?
Only about 1 in 20 babies arrives on the exact due date; most are born within two weeks either side. Think of it as the midpoint of a window, not a deadline.
▸What if I don't know my LMP?
An early ultrasound can date the pregnancy from the embryo's size. If you know your conception date, your due date is approximately 266 days after it.