Naegele's Rule: EDD = LMP + 280 days (40 weeks). Adjusted for longer/shorter cycles: add/subtract the difference from 28 days. If you know your exact conception date, EDD = conception + 266 days.
Pregnancy is measured in weeks + days (0w0d → 42w0d).
Full term: 39–40 weeks. Late term: 41 weeks. Post-term: >42 weeks (labour usually induced).
±2 weeks variation is normal — only ~5% babies arrived on the exact EDD.
India tip: register at your nearest Anganwadi/ANM sub-centre for PMVVY (₹5,000) and Janani Suraksha Yojana. Free institutional delivery + JSY cash assistance are available at government hospitals.