What a pregnancy calculator can't tell you
EDDs are estimates, not promises. Here's what the math leaves out — and when to lean on a clinician instead.
3 min readReviewed May 1, 2026
Quick answer
Only about 5% of babies arrive on the EDD. The calculator gives you a date to plan around, not a deadline. Anything clinical needs your provider.
What it doesn't model
- Multiples (twins, triplets) often arrive earlier than the EDD.
- Medical conditions that change recommended delivery timing.
- Personal history of preterm or post-term birth.
- IVF timing and embryo age, which use a different calculation.