What does “12 weeks” mean on this page?
If the last menstrual period was 84 days before the reference date, 84 ÷ 7 is 12.0 weeks. The page floors a backward date at zero, so it will not show negative weeks.
The method assumes you know the first day of that period. Entering a later day makes the estimate shorter than the usual last-period count.
Why a scan can disagree
A long or short cycle, an uncertain date, or an ultrasound measurement can date a pregnancy differently. For care, the clinician’s date is the one that matters.
This article does not explain symptoms, tests, or treatment. Pain, bleeding, or doubt about a date should go to a qualified clinician, not to a formula.
What the page refuses to invent
There is no due date, no 280-day addition, and no stored health record. The dates stay in the browser for that calculation.
If you only need the number of days, the date-difference calculator returns whole days without dividing by 7.
Questions
Is this a due-date calculator?
No. It only divides days since the last menstrual period by 7.
Which day should I enter?
The first day of the last menstrual period.
Does the page give medical advice?
No. It is approximate arithmetic for learning.