Guide
Pregnancy dating at a glance
How due dates and gestational age are estimated from LMP, ultrasound, conception, or IVF — and why exact birthday prediction is rare.
Pregnancy dating usually follows gestational age counted from the first day of the last menstrual period (LMP), not from the moment of fertilization.
Common anchors
- LMP + 280 days — classic estimated due date
- Conception + ~266 days — fertilization-based estimate
- Ultrasound — measure growth age at the scan, then project forward
- IVF transfer — known embryo age makes dating more precise
Term windows
Clinicians talk about early term, full term, late term, and postterm spans inside roughly 37–42 weeks. The due date is a midpoint in that range — only a small share of births land on the exact day.
Calcuit tools
| Question | Tool |
|---|---|
| What is my estimated due date? | Due Date Calculator |
| What week / trimester am I in? | Pregnancy Calculator |
| When might ovulation be? | Ovulation Calculator |
These calendars are educational aids. Confirm dating and care plans with your clinician.
References
Sources consulted while preparing this article. Links may lead to third-party sites.
- Due Date Calculator — Calculator.netLMP, ultrasound, conception, and IVF dating methods.
- Pregnancy Calculator — Calculator.netGestational age windows and due-date uncertainty.
- How accurate are 'due dates'? — BBC (Moore, 2015)