Estimate your due date and current pregnancy week from the first day of your last menstrual period (LMP).
Educational use only. This calculator is a general-purpose tool and does not replace medical advice. If a result surprises you or you have an underlying condition, consult a clinician before acting on it.
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The most widely used estimate, Naegele rule, adds 280 days (40 weeks) to the first day of your last period to predict the due date. It assumes a regular 28-day cycle with ovulation on day 14. About 5% of babies arrive exactly on the estimated date — the rest arrive within a two-week window before or after.
This calculator also reports your current pregnancy week and trimester. Your clinician will refine the date with an ultrasound, especially if your cycles are irregular. The first-trimester scan (typically at 8–12 weeks) is the most accurate way to date a pregnancy.
The trimesters split: first trimester ends at 13 weeks, second runs 14 to 26 weeks, third runs 27 weeks until delivery. Different things happen in each trimester and many prenatal milestones (screening tests, anatomy scan, glucose tolerance test) are tied to specific weeks.
Within about a week for women with regular 28-day cycles. For irregular cycles or unknown LMP, an early ultrasound is more accurate.
Because conception date is rarely known precisely, while LMP usually is. The 280-day count actually includes about two weeks before conception — a quirk of the convention.
Most clinicians will discuss induction options once you pass 41–42 weeks. The exact protocol varies by country and provider.
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