Pregnancy Week Calculator
Calculate pregnancy weeks
Frequently Asked Questions
How do I calculate what week of pregnancy I am in?
Count from the first day of your last menstrual period (LMP). Week 1 starts on your LMP date, not conception. At 4 weeks you've missed your period. At 12 weeks you finish the first trimester. The calculator shows your exact week and day.
What happens during each week of pregnancy?
Key milestones: Week 5: heartbeat detectable. Week 8: all major organs forming. Week 12: end of first trimester, risk drops. Week 20: anatomy scan, may learn sex. Week 24: viability milestone. Week 37: full term. Week 40: due date.
How do I convert pregnancy weeks to months?
Roughly: Weeks 1-4 = Month 1. Weeks 5-8 = Month 2. Weeks 9-13 = Month 3. Weeks 14-17 = Month 4. Weeks 18-22 = Month 5. Weeks 23-27 = Month 6. Weeks 28-31 = Month 7. Weeks 32-35 = Month 8. Weeks 36-40 = Month 9.
Why is pregnancy counted from the last period and not conception?
Because the exact conception date is usually unknown. LMP is a reliable, known date. Ovulation typically occurs around day 14 of a 28-day cycle, so "week 1-2" of pregnancy is actually before conception. This convention is used universally in obstetrics.
What size is my baby at each pregnancy week?
Week 8: raspberry (1.6 cm). Week 12: lime (5.4 cm). Week 16: avocado (11.6 cm). Week 20: banana (16.5 cm). Week 24: corn (30 cm). Week 28: eggplant (37.6 cm). Week 36: honeydew (47.4 cm). Week 40: watermelon (51.2 cm, ~3.5 kg).