All calculators
Health & Wellbeing2 min check
Pregnancy Due Date Calculator
Step 1 of 10%
How it works
Naegele's rule: due date = LMP + 280 days (40 weeks). For longer/shorter cycles, add or subtract the difference from 28 days. From a known conception date, due date = conception + 266 days (38 weeks).
Worked example
LMP: 1 January 2026, 28-day cycle.
- EDD = 1 Jan + 280 days = 8 October 2026
Who should use this
- •Newly pregnant women working out the EDD
- •Partners and families counting weeks
- •Anyone curious about trimester timing
Common mistakes
- ×Counting from conception assuming it's the same as LMP (it's ~14 days later)
- ×Forgetting cycle-length adjustments for irregular cycles
- ×Treating the EDD as a hard deadline — full term is 37-42 weeks
- ×Using LMP if you're unsure — a dating scan is more accurate
Frequently asked questions
How accurate is a due date?▾
Naegele's rule is ±2 weeks for most pregnancies. A first-trimester scan is accurate within ±5 days.
What if my cycle isn't 28 days?▾
Add (cycle - 28) days. So a 32-day cycle pushes the EDD by 4 days later.
When does each trimester start?▾
T1: weeks 1-12; T2: weeks 13-26; T3: weeks 27-40.
What if my baby is overdue?▾
Up to 42 weeks is normal. Most UK trusts offer induction discussion at 41 weeks.
Is conception the same as LMP?▾
No — conception is usually about 14 days after LMP in a 28-day cycle.