Pregnancy Due Date Calculator
Based on the first day of your last menstrual period (LMP), adjusted for cycle length.
Estimated due date
You're likely due on
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Weeks pregnant
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Trimester
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Days until due
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Conception date (est.)
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How due dates are estimated
Doctors use Naegele's rule: count 280 days (40 weeks) from the first day of the last menstrual period. It assumes a 28-day cycle and ovulation on day 14, with conception around day 14.
If your cycle is longer or shorter, ovulation shifts, and so does the due date. This calculator adjusts: a 30-day cycle adds 2 days; a 26-day cycle subtracts 2.
Only ~4% of babies arrive on their due date
The due date is an estimate, not a deadline. About 80% of babies arrive between 38 and 42 weeks — anywhere within a 4-week window is "on time." Most providers won't intervene before 41–42 weeks unless there's a specific concern.
Ultrasound is more accurate
A first-trimester ultrasound is the gold standard for dating — it measures the fetus directly. If yours suggests a date different from this calculator's, trust the ultrasound.
Estimate — not medical advice
Estimated due dates are approximate. Only about one birth in twenty happens on the predicted date. A dating ultrasound is considerably more accurate than any formula, and your provider's date should override this one.
This is an estimate, not medical advice, and not a diagnosis. It doesn't know your history, your medications, or your other results, and it should never be used to start, stop, or change treatment. If a number here concerns you, take it to a doctor or pharmacist rather than acting on it.