Practical guide
Pregnancy calendar guide
How to read a pregnancy calendar, count gestational weeks, and track development.
This information does not replace medical advice. Consult a healthcare professional for fertility or pregnancy questions.
Gestational weeks vs conception
Healthcare providers count pregnancy from the first day of your last menstrual period (LMP), not from conception. That's why "week 4" begins before implantation. A full-term pregnancy is about 40 gestational weeks (280 days from LMP).
Calculating your due date
Naegele's rule: LMP + 280 days. Only about 5% of babies arrive on the exact EDD — a range of 2 weeks before to 2 weeks after is normal. Use our due date calculator for an estimate.
Trimesters at a glance
- 1st trimester (weeks 1–13): organ formation, fatigue, nausea.
- 2nd trimester (weeks 14–27): growth spurt, often more energy, anatomy scan.
- 3rd trimester (weeks 28–40): weight gain, lung maturation, birth preparation.
Following week by week
Our pregnancy weeks hub covers all 40 weeks with baby size comparisons, maternal changes, and practical tips. Cross-check with your midwife or OB for personalized milestones and screenings.