Baby & Parenting
Pregnancy week calculator
Last period → pregnancy week, trimester and due date.
- Instant
- Free
- Private (processed locally)
- No sign-up
Calculate your pregnancy week
Enter the date of your last period: the tool gives the gestational age, trimester, due date and days remaining.
Reference
- Counted from the 1st day of LMP
- Due date = LMP + 280 days (40 weeks)
- T1 ≤ 13 wk, T2 14–27 wk, T3 ≥ 28 wk
- Indicative — the ultrasound is definitive
Indicative estimate. 100% local calculation.
Frequently asked questions
How are weeks counted?
Gestational age is counted from the first day of the last period (LMP), not from conception. Today − LMP gives the weeks + days.
When is the due date?
At 40 weeks, i.e. LMP + 280 days (Naegele’s rule). Only ~5% of babies arrive exactly on that date.
How are trimesters defined?
1st trimester up to 13 weeks, 2nd from 14 to 27 weeks, 3rd from 28 weeks.
Is it accurate?
It is an estimate based on a 28-day cycle. The dating ultrasound remains the reference.