Pregnancy Due Date Calculator
Estimated delivery date from LMP.
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This calculator gives a general estimate and isn't medical advice. It doesn't account for your individual health history — talk to a doctor before making decisions based on it.
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Formula
Due date = first day of last menstrual period (LMP) + 280 days
Naegele's rule assumes a 28-day cycle with ovulation on day 14, so gestation is counted as 40 weeks (280 days) from the LMP start date.
Worked example
With LMP on 1 January 2026, the estimated due date is 7 October 2026 — 280 days (40 weeks) later by Naegele's rule.
Where this can give the wrong answer
- Irregular cycles, late ovulation, or conception shortly after a bleed make LMP-based dating less accurate — early ultrasound dating often overrides this estimate clinically.
- Only about 4–5% of births occur on the exact calculated due date; 'term' spans roughly 37–42 weeks.
- Gestational age shown is approximate from today's date and will change daily; it's a snapshot, not a fixed milestone.
FAQ
- Clinical pregnancy length is measured in weeks (40), not months. Calendar months vary from 28 to 31 days, so 9 months would be ambiguous — 280 days from LMP is the standard obstetric convention.