Due Date Calculator
Enter the first day of your last menstrual period (LMP) to estimate your due date, how far along you are, and which trimester you are in.
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Frequently asked questions
How is the due date calculated?
The standard obstetric estimate adds 280 days (40 weeks) to the first day of your last menstrual period (LMP). This assumes a 28-day cycle with ovulation around day 14, which is the convention used by most due-date calculators and clinics.
Is my due date an exact birth date?
No. Only about 4–5% of babies arrive exactly on the due date. A normal, healthy pregnancy can safely last anywhere from 37 to 42 weeks, so think of the due date as a midpoint of a multi-week window.
What if my cycles are longer or shorter than 28 days?
This calculator uses the standard 28-day assumption. If your cycle is irregular or noticeably longer, an early ultrasound dating scan gives a more personalized estimate — ask your provider.