📖 Overview
Calculate your expected due date and current pregnancy week based on your last menstrual period date.
⚙️ How It Works
Uses Naegele's rule — the standard obstetric method — to estimate the expected date of delivery (EDD) by adding 280 days (40 weeks) to the first day of the last menstrual period (LMP).
The Formula
EDD = LMP + 280 days
| LMP | First day of the last menstrual period (entered as year, month, day) |
| 280 days | 40 weeks — average length of human pregnancy from LMP |
| EDD | Estimated Due Date (expected date of delivery) |
⚠️This is an estimate only. Due dates can shift based on ultrasound measurements, cycle length, and other clinical factors. Always confirm with your healthcare provider.
Quick Reference
| Weeks pregnant | Trimester | Milestone |
|---|---|---|
| 1–12 | First | Organ formation, heartbeat detectable ~6 weeks |
| 13–26 | Second | Movement felt, gender visible on ultrasound |
| 27–40 | Third | Rapid growth, lung maturation, birth preparation |
| 37–40 | Full term | Baby is considered full term from week 37 |
Practical Tips
💡 For irregular cycles, your doctor may adjust the EDD based on early ultrasound dating.
💡 Only about 5% of babies are born exactly on their due date — most arrive within 2 weeks either side.
💡 The calculator also shows current pregnancy week, which is useful for tracking milestones.
Frequently Asked Questions
❓ Why does pregnancy count from the last period, not conception?
Conception date is rarely known precisely, but the LMP is easily remembered and used as a standard reference point.
❓ What is considered full term?
37 to 42 weeks gestation. Before 37 weeks is preterm; after 42 weeks is post-term.
❓ Is my due date a guaranteed delivery date?
No. It is a statistical average. Only about 5% of births happen on the exact due date.