Pregnancy Due Date Calculator
Estimate a due date from the last menstrual period or conception date.
An estimate using a standard formula, not medical advice — only about 5% of babies arrive on their exact due date. Your care provider's estimate (often based on an early ultrasound) is more accurate than this calculation alone.
Estimated due date
Tuesday, June 22, 2027
Gestational age
0w 0d
Trimester
1st
For informational and educational purposes only — not medical advice, and not a substitute for consulting a qualified professional about your specific situation. TrueMeasureKit is not liable for decisions made based on these results. See our Terms of Service.
Where 280 days comes from
Naegele's rule — the standard estimate used by most due-date calculators — adds 280 days (40 weeks) to the first day of the last menstrual period. It assumes a textbook 28-day cycle with ovulation on day 14, which is why calculating from a known conception date instead (adding 266 days) can be more accurate for people with longer or shorter cycles. Either way, this is a statistical estimate: a full-term pregnancy spans a range of about three weeks around this date, not a fixed deadline.
Frequently asked questions
How is the due date estimated?
Using Naegele's rule: adding 280 days (40 weeks) to the first day of the last menstrual period, or the equivalent offset from a known conception date. This is the same standard method used by most obstetric providers for an initial estimate.
How accurate is a due date estimate?
Only about 5% of babies are born exactly on their estimated due date — most arrive within a couple of weeks before or after. An early ultrasound typically gives a more precise estimate than menstrual-cycle dating alone.