Quick answer: pregnancy weeks are counted from the first day of your last menstrual period, not from conception. Use our free Pregnancy Due Date Calculator to see your current week and due date.
Why Weeks Are Counted This Way
Since the exact conception date is rarely known, doctors date pregnancy from the last period's start — meaning "week 4 pregnant" is really only about 2 weeks post-conception.
Key Milestones by Week
Weeks 1-13 make up the first trimester, weeks 14-27 the second, and weeks 28-40+ the third, each with its own typical developmental and screening milestones.
Frequently Asked Questions
Why does my due date shift after an ultrasound?
Early ultrasounds can more precisely date the pregnancy than a calendar estimate, sometimes adjusting the due date by a few days.
Is 40 weeks exact?
No — it's an average; full-term birth is generally considered anywhere from 37 to 42 weeks.
Should I use this instead of my doctor's estimate?
Use this as a quick reference; always defer to your healthcare provider's clinical estimate.
✨ Try it now — free & instant
Open the Tool →