How to work out how many weeks pregnant you are
- Choose your starting point: the first day of your last period is the standard.
- Enter the date and, if needed, your usual cycle length.
- See how many weeks and days pregnant you are today, your trimester, due date and a milestone timeline with dates.
How pregnancy weeks are counted
Doctors and midwives count pregnancy from the first day of your last menstrual period, not from conception. That means you are already about two weeks pregnant at conception and around four weeks when a home test first turns positive. A full-term pregnancy is about 40 weeks. "8 weeks 3 days" means eight full weeks and three days have passed since that starting point.
The first trimester runs to the end of week 13, the second from week 14 to the end of week 27, and the third from week 28 until birth. If your cycles are irregular or you are unsure of your period date, an early ultrasound gives the most reliable dating; enter the scan result to use it here. Your dates stay in your browser unless you share the link.
ℹ️ Not medical advice: an estimate for healthy adults. Ask a doctor or qualified professional about your own situation.
FAQ
When does the second trimester start?
At 14 weeks 0 days.
Why am I two weeks pregnant at conception?
Pregnancy is dated from the last period, about two weeks before ovulation.
How many months is 40 weeks?
About nine calendar months plus one week.